U.S. patent number 5,052,777 [Application Number 07/266,458] was granted by the patent office on 1991-10-01 for graphics display using bimorphs.
This patent grant is currently assigned to Sportsoft Systems, Inc.. Invention is credited to Volker Bodegom, Ralph Dyck, Allen Miller, Ronald M. Ninnis.
United States Patent |
5,052,777 |
Ninnis , et al. |
October 1, 1991 |
Graphics display using bimorphs
Abstract
A bimorph using ultraviolet setting glue to laminate a
piezoelectric film structure, having etched-back metalization
patterns on the surfaces of the piezoelectric film. The bimorph is
used in a bimorph light modulator including a substrate on which
fiber optic input and output light guides are mounted. A gap
between the light guides serve as an optical coupling. A bimorph is
affixed to the substrate with a shutter attached to one end thereof
and positioned within the gap for blocking the light coupling when
the bimorph is in the unenergized state. When the bimorph is
energized, it pulls the shutter out of the gap, thereby allowing
light coupling. Top and bottom stops are used to limit the bimorph
movement to damp resonant vibrations and improve on and off times.
Viscous air damping is used to eliminate or minimize bounce of the
top and bottom stops and to help damp resonant vibration. An array
of the bimorphs may be utilized for providing a video or other
display, with electrode connections being made to the bimorphs by
means of conductors which contact the bimorph electrodes at small
surface areas, with the conductors being attached to circuit boards
carrying signals for operating the bimorph array. The optical
fibers may be coupled to different light sources and filters to
provide color images, and groups of optical fibers may be arranged
to form pixels for providing a broad range of intensities.
Inventors: |
Ninnis; Ronald M. (Vancouver,
CA), Miller; Allen (Langley, CA), Dyck;
Ralph (Vancouver, CA), Bodegom; Volker (Fort
Langley, CA) |
Assignee: |
Sportsoft Systems, Inc.
(Burnaby, CA)
|
Family
ID: |
26883777 |
Appl.
No.: |
07/266,458 |
Filed: |
November 2, 1988 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
188153 |
Apr 27, 1988 |
4844577 |
Jul 4, 1989 |
|
|
944695 |
Dec 19, 1986 |
|
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Current U.S.
Class: |
385/19; 359/230;
310/332 |
Current CPC
Class: |
G02B
26/08 (20130101); G02B 6/358 (20130101); G02B
6/3552 (20130101); G02B 6/3578 (20130101); G02B
6/353 (20130101); G02B 6/3566 (20130101) |
Current International
Class: |
G02B
6/35 (20060101); G02B 26/08 (20060101); H01L
41/09 (20060101); G02B 006/24 () |
Field of
Search: |
;350/96.29,96.14,96.20 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Toda, "Design of Piezoelectric Polymer Motional Devices with
Various Structures", Transactions of the IECE of Japan, vol. E61,
No. 7, Jul. 1978. .
Toda and Osaka, "Application of PVF.sub.2 Biomorph Cantilever
Elements to Display Devices", Proceedings of the S.I.D., vol. 19/2,
Second Quarter 1978. .
Toda and Osaka, "Large Area Electronically Controllable Shutter
Array Using PVF.sub.2 Biomorph Vanes", Ferroelectrics, 1980, vol.
23, pp. 121-134. .
Frank and Lee, "Piezoelectric Camera Shutter", Research Disclosure,
7 Sep. 1978. .
Frank and Lee, "Piezoelectric Shutter Control for Camera", Research
Disclosure, Jun. 1978. .
Toda, "Voltage Induced Large Amplitude Bending Device/PVF.sub.2
Biomorph--Its Properties and Applications", Ferroelectrics, 1981,
vol. 32, pp. 127-133. .
Stephany and Gates, "Biomorph Optical Beam", Applied Optics, Feb.
1976, Bol 15, No. 2, pp. 307-308. .
Keuning, "A Mixed Boundary Value Problem for an Infinite,
Piezoceramic Bimorph", Acta Mechanica, 14, 199-217 (1972). .
Toda and Osaka, "Electromotional Device Using PVF.sub.2 Multilayer
Biomorph", Transactions of the IECE of Japan, vol. E61, No. 7, Jul.
1978. .
Toda, Osaka, and Johnson, "A New Electromotional Device", RCA
Engineer, 25-1, Jun./Jul. 1979, pp. 24-27. .
Chatigny, "Piezo Film Yields Novel Transducers", Electronics Week,
Aug. 6, 1984, pp. 74-77. .
Toda, Osaka, Tosima, "Large Area Display Element Using PVF.sub.2
Biomorph with Double Support Structure", Ferroelectrics, 1980, vol.
23, pp. 115-120. .
Carome and Koo, "PVF.sub.2 Phase Shifters and Modulators for Fiber
Optic Sensor Systems", 1980, IEEE Triplesonics Symposium, pp.
710-712..
|
Primary Examiner: Lee; John D.
Assistant Examiner: Heartney; Phan T.
Attorney, Agent or Firm: Fish; Ronald C.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This is a continuation-in-part of U.S. patent application Ser. No.
188,153, filed Apr. 27, 1988 (now U.S. Pat. No. 4,844,577, issued
July 4, 1989) which is a File Wrapper Continuation of U.S. patent
application Ser. No. 944,695 filed on date Dec. 19, 1986 (now
abandoned).
Claims
What is claimed is:
1. An apparatus for generating visual display information from
input signals, comprising:
an illumination source;
a substrate;
a plurality of first optical fibers mounted on said substrate, each
said first optical fiber having a first input end and a first
output end, with said first input ends coupled to said illumination
source for transmitting light from said source to said first output
ends;
a plurality of bimorph gate means mounted on said substrate, for
individually modulating the intensity of light from said
illumination source which exits each of said plurality of first
optical fibers by selective placement of a shutter in front of said
first output ends with one said bimorph gate means adjacent each
said first optical fiber, each said bimorph gate means including a
bimorph having a shutter, wherein each said bimorph is translatable
between a first position for causing said shutters to block said
light at said first output ends and a second position for
maintaining said shutter away from said first output ends for
allowing said light to be transmitted from said first output
ends;
a plurality of second optical fibers, each said second optical
fiber having a second input end and a second output end, wherein
said second input ends are optically coupled to said first output
ends, and wherein said shutters are interposed between said first
output ends and said second input ends when said bimorph gate means
are in said first portions; and
means for translating said bimorph gate means between said first
positions and said second positions in response to the input
signals, such that said second optical fibers transmit the visual
information to said second output ends, wherein a plurality of said
second optical fibers carry information relating to a single visual
pixel of the visual information, each said pixel having an
intensity and/or color controlled by how many of said bimorph gate
means are in said first position at said first input ends of said
second optical fibers relating to said pixel.
2. The apparatus of claim 1, further comprising a plurality of
optical fibers interposed between said illumination source and said
first input ends for selectively transmitting light of different
colors, such that each said pixel generates a portion of the visual
information relating to at least one said color.
3. The apparatus of claim 1, wherein each said bimorph gate means
gate includes a top stop for limiting the range of movement of said
bimorph and to damp resonant vibrations of said bimorph when in
close proximity with said top stop.
4. The apparatus of claim 1, wherein each said bimorph gate means
includes a first electrode and a second electrode, and wherein each
said translating means is coupled to one said bimorph so as to
provide said first electrode with a first potential and said second
electrode with a second potential, with said first and second
potentials being relating to said input signals.
5. The apparatus of claim 4, wherein each said bimorph gate means
comprises:
a first piezoelectric film having a first surface and a second
surface, said first and second surfaces being metalized; and
a second piezoelectric film having a third surface and a fourth
surface, said third and fourth surfaces being metalized, said first
and second films being laminated together with said second surface
and said third surface being electrically coupled, wherein said
second film includes a portion extending beyond said first film
when said films are laminated together, thus exposing said third
surface, and wherein said translating means provides said first
potential to said exposed third surface and provides said second
potential to said first and fourth surfaces.
6. An apparatus for controlling intensity of light transmitted
through an optical fiber in response to input signals relating to
visual information, comprising:
a substantially rigid template including first, second and third
grooves, said second and third grooves being substantially parallel
to one another with said first groove intersecting said second
groove at a first intersection and further intersecting said second
groove at a second intersection;
a bimorph fixed within said first groove and having a first end
protruding from said template, said bimorph having a first
electrode, a second electrode, and a shutter attached to said first
end, said bimorph being movable between a first position and a
second position, wherein said shutter blocks the light when said
bimorph is in said first position and passes the light when said
bimorph is in said second position;
a first conducting strip positioned within said second groove in
electrical contact with said first electrode;
a second conducting strip positioned within said third groove in
electrical contact with said second electrode;
a circuit board positioned on top of said first and second strips
for providing a first potential to said first strip and a second
potential to said second strip, with said first and second
potentials relating to the input signals, for controlling the
movement of said bimorph between said first position and said
second position; and
means for maintaining said template, said bimorph, said first and
second conducting strips, said circuit board, and the optical fiber
in a substantially fixed relationship.
7. The apparatus of claim 6, wherein said template further includes
a first ridge at said first intersection and a second ridge at said
second intersection, for cooperating with said circuit board to
provide localized pressure to said first and second intersections,
respectively, when said circuit board is fixed in place by said
maintaining means.
8. The apparatus of claim 6, wherein first groove has a forward end
including beveled edges for facilitating placement of said bimorph
within said first groove and wherein said first and second
conducting strips are elastomeric and wherein said means for
maintaining compresses said first and second conducting strips
approximately 30%.
9. An apparatus for controlling transmission of light,
comprising:
a substrate;
transmitting means, carried by said substrate, for transmitting the
light;
at least one bimorph having a first piezoelectric layer and a
second piezoelectric layer in a laminate structure, forming first,
second and third electrodes, where said first electrode is formed
on an outside surface of said first layer, said second electrode is
formed at a lamination junction between said first and second
layers, and said third electrode is formed on an outside surface of
said second layer, said bimorph having a shutter at a forward end
thereof for blocking light emitted from said transmitting means
when said bimorph is not activated;
first, second and third energizing means for energizing said first,
second and third electrodes, respectively;
first, second and third means for providing signals to said first,
second and third energizing means, respectively, for activating
said bimorph;
means for maintaining said energizing means in contact with said
electrode; and
wherein said first energizing means comprises a first printed
circuit board having at least one first ground trace and first
connecting means for electrically connecting said ground trace to
said first electrode.
10. The apparatus of claim 9, wherein said second energizing means
comprises a second printed circuit board having at least one high
voltage trace connected to a high voltage source, with one said
high voltage trace for providing signals for activating each said
bimorph, and further comprises second connecting means for
electrically connecting said high voltage trace to said second
electrode.
11. The apparatus of claim 10, wherein said third energizing means
comprises at least one second ground trace disposed on said second
printed circuit board and third connecting means for electrically
connecting said second ground trace to said third electrode.
12. The apparatus of claim 11, wherein each of said first, second
and third connecting means comprise first, second and third
resilient electrical connectors, respectively, for contacting a
first area of each of said first, second and third electrodes,
respectively, where each said first area is less than a total area
of each of said first, second and third electrodes.
13. The apparatus of claim 12, wherein each of said first, second
and third connecting means is maintained in tight contact with each
of said first, second and third electrodes, respectively, such that
a fluid-tight seal is formed at each said contact.
14. The apparatus of claim 12, wherein each said first connector
comprises a portion of a substantially homogeneous conductive strip
having a longitudinal direction extending transversely to a
longitudinal direction of each said first electrode of each said
bimorph.
15. The apparatus of claim 12, wherein each said second connector
comprises a portion of a strip which is nonconductive in a
longitudinal direction thereof, but is conductive in directions
substantially orthogonal to said second connector longitudinal
direction.
16. The apparatus of claim 12, wherein each said third connector
comprises a portion of a substantially homogeneous conductive strip
having a longitudinal direction extending transversely to a
longitudinal direction of each said third electrode of each said
bimorph.
17. The apparatus of claim 12, wherein each said third connector
comprises a portion of a strip which is nonconductive in a
longitudinal direction thereof, but is conductive in directions
substantially orthogonal to said third connector longitudinal
direction.
18. The apparatus of claim 12, wherein:
each said first connector comprises a first conductive button
carried by said first printed circuit board;
each said second connector comprises a second conductive button
carried by said second printed circuit board; and
each said third connector comprises a third conductive button
carried by said second printed circuit board.
19. The apparatus of claim 18, wherein each of said first, second
and third conductive buttons has a diameter which is substantially
equal to a diameter of said first, second and third electrodes,
respectively.
20. The apparatus of claim 18, wherein each of said first, second
and third conductive buttons has a diameter which is less than a
diameter of said first, second and third electrodes,
respectively.
21. The apparatus of claim 18, wherein each of said first, second
and third conductive buttons has a surface area which is less than
a surface area of each of said first, second and third electrodes,
respectively.
22. The apparatus of claim 12, wherein said first, second and third
connecting means and said bimorph are mounted between said first
and second printed circuit boards, and wherein said apparatus
further comprises means for maintaining said first and second
printed circuit boards in a fixed relationship for maintaining
electrical contact between each of said first, second and third
connecting means and each of said first, second and third
electrodes, respectively.
23. The apparatus of claim 22, wherein said maintaining means
comprises:
holes in said second printed circuit board, each said hole having a
first diameter and a second diameter which is larger than said
first diameter;
a rivet aligned with each said hole and carried by said substrate,
wherein said rivet is adapted for binding said first and second
printed circuitboards together by an enlarged end thereof which is
larger in diameter than said first hole diameter and is smaller in
diameter than said second hole diameter.
24. An apparatus for generating visual display information from
input signals, comprising an illumination source and at least one
bimorph shelf, wherein each said bimorph shelf comprises:
a substrate;
a plurality of optical fibers mounted on said substrate, each said
optical fiber having an input end and an output end, with said
input ends coupled to said illumination source for transmitting
light from said source to said output ends; and
a plurality of bimorph gates mounted on said substrate, with one
said bimorph gate adjacent each said optical fiber, each said
bimorph gate including a bimorph having a shutter, wherein each
said bimorph is translatable between a first position for causing
said shutters to block said light at said output ends and a second
position for maintaining said shutter away from said output ends
for allowing said light to be transmitted from said output
ends;
wherein said apparatus further comprises means for translating said
bimorphs between said first positions and said second positions in
response to the input signals, and optical display means coupled to
said output ends for displaying visual information carried by said
optical fibers, wherein said shutters are positioned between said
output ends and said display means when said shutters are in said
first position.
25. The apparatus of claim 24, wherein a plurality of said optical
fibers carry information relating to a single visual pixel of the
visual information, each said pixel having an intensity controlled
by how many of said bimorphs are in said first position at said
input ends of said optical fibers relating to said pixel.
26. The apparatus of claim 25, wherein said apparatus comprises a
plurality of said bimorph shelves in an array, and each said pixel
is formed by said output ends of optical fibers carried by at least
two said bimorph shelves which are adjacent one another in said
array.
27. The apparatus of claim 24, wherein each said gate includes a
top stop for limiting the range of movement of said bimorph and to
damp resonant vibrations of said bimorph when in close proximity
with said top stop.
28. The apparatus of claim 27, wherein each said bimorph includes a
first electrode and a second electrode, and wherein each said
translating means is coupled to one said bimorph so as to provide
said first electrode with a first potential and said second
electrode with a second potential, with said first and second
potentials being relating to said input signals.
29. The apparatus of claim 28, wherein each said bimorph
comprises:
a first piezoelectric film having a first surface and a second
surface, said first and second surfaces being metalized; and
a second piezoelectric film having a third surface and a fourth
surface, said third and fourth surfaces being metalized, said first
and second films being laminated together with said second surface
and said third surface being electrically coupled, wherein said
second film includes a portion extending beyond said first film
when said films are laminated together, thus exposing said third
surface, and wherein said translating means provides said first
potential to said exposed third surface and provides said second
potential to said first and fourth surfaces.
30. The apparatus of claim 24, further comprising at least one
optical filter for transmitting light of at least one color, such
that each said fiber transmits a portion of the visual information
relating to at least one said color.
31. The apparatus of claim 30, wherein said optical filter is
interposed between said illumination source and said input
ends.
32. The apparatus of claim 30, wherein said optical fiber is
interposed between said output ends and said display means.
33. The apparatus of claim 32, wherein said optical fibers are
configured to form a first array, and said optical filter comprises
a second array of filter windows, wherein said second array
conforms to said first array such that each of said optical fiber
output ends is optically coupled to one said filter window.
34. The apparatus of claim 33, wherein a first portion of said
filter windows of said second array are of a first color and a
second portion of said filter windows of said second array are of a
second color.
35. The apparatus of claim 34, wherein said first and second
portions of said filter windows are positioned in said second array
so as to form a third array comprising pixels, each said pixel
including one filter window from each of said first and second
portions.
36. The apparatus of claim 34, wherein a third port of said filter
windows are of a third color and said first, second and third
portions of said filter windows are positioned in said second array
so as to form a third array comprising pixels, each said pixel
including one filter window from each of said first, second and
third portions.
37. The apparatus of claim 36, wherein a fourth portion of said
filter windows are of a fourth color and said third array includes
said fourth portion of said filter windows, such that each said
pixel includes one filter window from each of said first, second,
third and fourth portions.
Description
BACKGROUND OF THE INVENTION
The invention pertains to the field of bimorphs in general, and
more particularly, to the field of bimorph based light
modulators.
Bimorphs are not new devices. Basically, a bimorph is a device
manufactured with two strips of piezoelectric film which are
fastened together and which have electrodes allowing electrical
fields of the proper polarity to be applied through the film to
cause an electrostrictive effect to occur. This electrostrictive
effect changes the dimensions of the film of the two different
strips in such a way that the bimorph bends.
Bimorphs have been used in the prior art to modulate light by using
the bimorph to bend into and out of the path of a light beam. The
physical occlusion of the light path by the bimorph interrupts the
light beam and therefore modulates the light in accordance with the
timing and intensity of the electrical fields applied to the
bimorph. Bimorphs have also been used in the prior art to interrupt
the light path at the focal point between two lenses, and have been
used to trip the shutter mechanisms of cameras when a sufficient
amount of light for proper exposure has been received. It is known
in the prior art to attach a right angle shutter to a bimorph and
to allow the bimorph to bend into and out of the path of light
through an aperture in a mask plate. It is also known to use
bimorphs in display elements such as seven segment displays where
instead of using light-emitting diodes for each of the segments in
the display, a bimorph painted with a distinctive color is used to
activate each display segment. It is also known in the prior art to
doubly support the bimorph with a fixed fulcrum somewhere in the
middle of the length of the bimorph and a movable fulcrum on one
end thereby leaving one end of the bimorph free to move in response
to the applied electric fields.
It is also known in the prior art to use piezo film for its
piezoelectric property in order to manufacture transducers. That
it, when piezo film is subjected to mechanical stress, a voltage
can be generated which can be sensed to signal the occurrence of an
event causing the mechanical stress.
It is also known in the prior art to use bimorphs in conjunction
with a Mach-Zehnder optical interferometer to implement an optical
phase shifter in fiber optic sensor systems.
Other workers in the art have used bimorph light beam deflectors
wherein a mirror is placed at the end of a bimorph and a laser beam
is directed onto the mirror such that the angle of reflection is
altered by the bending of the bimorph. Still other workers in the
art have used bimorphs to implement a mechanical multiplexer for
fiber optic switching of light from one input fiber to either of
several output fibers.
There are certain problems which arise from the use of bimorph
cantilevered beams for the interrupting of light paths. For one,
the cantilevered beam has its own mechanical resonant frequency.
When such a beam is excited by a narrow pulse or a step function,
the beam bends and mechanical resonance or vibration often occurs,
causing the free end of the beam to vibrate. If the vibration
causes any portion of the bimorph or the shutter to move into and
out of a light path, errors in the desired average light flux will
occur. Further, when driving such a bimorph at high frequencies,
the acceleration of the beam and its velocity is high. If a
mechanical stop is used to limit the travel of the beam, the
bimorph can hit the mechanical stop and bounce. Such bouncing
action is called chatter and also causes errors in the average
light flux passing the bimorph since the light flux is calculated
under ideal conditions where no bounce occurs.
It is useful to use bimorph light modulators in large area displays
where each bimorph modulates the average light flux emerging from a
particular pixel location or from one color component of a pixel in
a three-primary-color pixel. Such displays have advantages over
conventional secondary emission displays in that a light source of
any desired intensity may be used to supply the input light which
may then be modulated using the individual bimorphs in accordance
with scene information to control the gray scale light intensity of
each pixel. The advantage of such an arrangement is that high
contrast and good visibility during high ambient light conditions
can be achieved. That is, the light emerging from the face of such
a display can be made much more intense than the light emerging
from secondary emission displays such as cathode ray tubes (CRTs)
and television type screens since phosphor light emission is
limited in intensity. In contrast, a display using bimorphs is not
limited in the intensity of the light at each pixel location by the
physical nature of any secondary emission type material such as
phosphor. Further, such a display can be made very large since the
light from the source can be directed to very large numbers of
pixels by optical channels such as fiber optic light guides, and
there is no need for deflecting an electron beam to raster scan the
entire display.
Use of bimorphs to control the pixel light intensities in a large
scale display requires very accurate correspondence between the
electronic signal which encodes the desired amount of light at each
pixel location and the actual average light flux which is gated
through to that location by the bimorph. Further, video displays
require vast quantities of data to be handled in very short times
if the display is to be compatible with NTSC and PAL television
signals. Thus, each bimorph must be able to operate at a fairly
high frequency and accurately control the average light flux
passing through the light channel controlled by that bimorph.
The bimorph structures taught in the prior art could not be used
for application to such a large scale display. For one thing, the
structures taught in the prior art suffer from resonance and
chatter problems which would degrade the accuracy and repeatability
in controlling the average light flux passing through the light
channel controlled by each bimorph. Further, the bimorph structures
taught in the prior art would suffer from electrostatic pinning
problems which would degrade the ability of the bimorph to operate
at high frequencies necessary to handle NTSC and PAL television
signals. The bimorph structures taught in the prior art would also
be unreliable since no means is taught for preventing the
electrostrictive dimensional changes of the bimorph film from
occurring at the locations of electrical contacts. Thus, the
electrical contacts can be rendered intermittent or be caused to
fail altogether by the mechanical stresses induced when the film
changes dimensions under the contact locations.
Further, the bimorphs of the prior art are generally glued together
with glues which render the assembly of the bimorph difficult. It
is important to be able to glue the two film strips together
without bubbles, wrinkles or other stress in the film which could
cause curl in the final structure. With the types of glue taught in
the prior art, only a limited amount of time is available before
the glue sets to adjust the two films and eliminate wrinkles, curls
and stresses. This would make assembly and registration of the two
films and removal of wrinkles, bubbles and other stress-producing
artifacts more difficult.
Further, the prior art does not teach a method of registering the
bimorph and shutter with a light path to insure that complete
occlusion of the light path will occur when the bimorph is in the
"off" position. Since bimorph film is extremely thin and is made of
polymer film, there is often curl in the final bimorph product
which varies from one bimorph to another. It is important to be
able to register all the bimorph shutter controlling elements at
the outset to insure that when all the bimorphs are in the "off"
position, the shutters for each bimorph completely occlude all
light paths, and none are in a prestressed state which is different
from the prestressed state of the others. If this is not the case,
each bimorph will act differently in response to the same
signal.
Accordingly, a need has arisen for a bimorph light modulator for
use in implementing large scale displays which can operate at high
enough frequency to be compatible with television signals and which
can control very high intensity light such that the display is
usable in high ambient light conditions with good contrast and
visibility. Further, such bimorphs must be relatively easy to
assemble, and must be reliable and accurate in terms of the
repeatability of the light intensity modulation which may be
achieved.
SUMMARY OF THE INVENTION
According to the teachings of the invention there is disclosed a
bimorph which is easier to manufacture than bimorphs taught in the
prior art. There is also disclosed a bimorph light modulator having
an improved design in that resonance and chatter effects are
minimized, and light modulation response is accurate and
repeatable. The bimorph light modulator of the preferred embodiment
uses fiber optic light guides so a single very bright source may be
used for input light and very large, bright, high contrast displays
may be manufactured. In alternative embodiments, other types of
input and/or output light guides may also be used. Further, the
device may be used in the ultraviolet or infrared spectrums, so
suitable radiation guides for light at these wavelengths may also
be used.
The bimorph is comprised of two piezoelectric films which are
laminated together with ultraviolet-setting glue. The film strips
have a predetermined set of metalization patterns on the various
surfaces thereof. These metalization patterns are registered with
each other and have unmetalized areas to eliminate dimensional
changes of the film under the electrical contact. The metalized
patterns are also formed away from the edges of the film to
eliminate the possibilities of shorts and to minimize electrostatic
pinning due to edge electrostatic fields. The purpose of the
metalization patterns is to allow electric fields of the
appropriate polarity be applied across the piezo film to cause the
desired electrostrictive bending for use in modulating light. In
alternative embodiments, electrostatic pinning may be avoided by
other configurations of the bimorph, the substrate and the
metalization patterns. To eliminate electrostatic pinning, it is
essential that the substrate be conductive and that the top and
bottom electrodes be conductive and connected to be at the same
potential. The substrate (and therefore the bottom metalization
pattern) and the top metalization pattern could then be at ground
with the center metalization pattern at high voltage as in the
preferred embodiment. An alternative embodiment could be used where
the center electrode is kept at ground potential and the substrate
and the top electrode driven to high voltage when bending is
desired. The high voltage electrode must be etched back in whatever
embodiment is used to eliminate the edge fields that cause
electrostatic pinning.
The light modulator according to the teachings of the invention is
constructed using an input light guide and an output light guide.
In alternative embodiments, no output light guide is necessary. In
the preferred embodiment, both the input and the output light
guides are fiber optic light guides. The output light guide has a
diameter three times as large as the diameter of the input light
guide. There is a gap between the output of the input light guide
and the input of the output light guide. This gap is the path of
coupling for light emerging from the input light guide and entering
the output light guide. The light guides are mounted on a substrate
and the bimorph is mounted on the substrate also in a predetermined
position so that it may used to modulate the light passing through
the gap. The bimorph has an aluminum film attached to one end
thereof to act as a shutter. The bimorph is mounted on the
substrate so as to register the shutter in the gap between the
input light guide and the output light guide. The shutter
registration position is selected to completely occlude coupling of
light between the light guides when the bimorph is in its uncurved
state. The side of the shutter facing the input light guide is
coated with a black, light absorbing coating to eliminate light
reflections back into the input light guide. When voltage is
applied to the bimorph, the bimorph curves and the shutter is
removed from the gap to allow light coupling between the light
guides.
The larger diameter of the output light guide maximizes the
efficiency of the light coupling and renders the size of the gap
noncritical within a certain range.
By varying the duty cycle of the applied voltage, the duty cycle of
the presence and absence of the shutter in the gap can be varied.
This controls the average light flux coupled between the light
guides, and after averaging by the human eye, the perceived effect
is a modulated average light intensity.
In the preferred embodiment, a bimorph of sufficient width to cause
viscous air damping is used. Also, a three point mechanical
mounting is used with a fulcrum in the midsection of the bimorph.
This causes the bimorph to form a shallow angle with the substrate
to prevent hydrostatic sticking. The three point mechanical
mounting is important in obtaining high registration tolerance of
the shutter with respect to the input light guide since perfectly
flat bimorphs cannot be manufactured. Top and bottom stops are used
to limit the range of movement of the bimorph to improve turn-on
and turn-off time and to damp resonant vibrations.
Also disclosed is a process for making the bimorph and a process
for mounting the bimorph to eliminate stresses in the bimorph and
to achieve accurate registration.
A particular feature of a preferred embodiment of the invention is
the utilization of electrical connecting means for the bimorphs and
printed circuit board electrodes which have small areas of contact,
so that the contacts are subjected to relatively high pressure for
a given force binding an array of bimorphs together. This ensures
reliable electrical contacts, and in addition seals the contacts
from the intrusion of gases, liquids, or other corrosive or
detrimental materials. The reduced-area contacts may be made by
means of electrically conduction strips (either homogeneous strips
or zebra strips) laid transversely to the respective electrodes, or
may be made by means of electrically conduction rubber buttons
mounted on printed circuit boards carrying means for energizing the
bimorphs.
An array of the bimorphs may be utilized for providing a video or
other display, and the optical fibers may be coupled to different
light sources and filters to provide color images. Groups of
optical fibers may be arranged to form pixels for providing a broad
range of intensities.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of one embodiment of a bimorph light
modulator using fiber optic light guides.
FIG. 2 is a perspective view of a bimorph light modulator according
to the preferred embodiment of the invention.
FIG. 3 is a perspective exploded view of a bimorph construction
according to the teachings of the invention.
FIG. 4 is a drawing showing the metalization patterns for the four
surfaces of one embodiment of a bimorph constructed in accordance
with the teachings of the invention.
FIG. 5 is a flow chart of the process of manufacturing a bimorph
according to the teachings of the invention.
FIG. 6 is a side view of one embodiment of the bimorph light
modulator at a point in the construction when the bimorph has been
shutter registered, and is ready to be fastened down for purposes
of making electrical connections.
FIG. 7 is a flow chart of the bimorph mounting process according to
the teachings of the invention.
FIG. 8 is a side elevation view of the registered position of the
bimorph in a prestressed embodiment to eliminate the effects of
elastic lag.
FIG. 9 is a side elevation view of another embodiment of the light
modulator of the invention having output optics which may be
attached readily by plugging the output optics module onto the
bimorph light modulator shelf.
FIG. 10 is a side view of the electrical connections of the bimorph
according to one embodiment.
FIG. 11 is a top view of an embodiment of the electrical
connections using conductive epoxy.
FIG. 12 is a top view of one embodiment of the shelf containing
multiple light modulators according to the teachings of the
invention.
FIG. 13 is a perspective view of an embodiment of a module
containing a plurality of the shelves shown in FIG. 12.
FIG. 14 is a block diagram of one type of electronic driver circuit
which can be used in conjunction with the light modulator according
to the teachings of the invention.
FIG. 15 is an exploded view of the construction of a bimorph
according an alternative embodiment of the invention.
FIG. 16 shows the alternative embodiment of the bimorph of FIG.
15.
FIG. 17 is a cross-sectional view taken along line 17--17 of FIG.
16.
FIG. 18 is an exploded view of an alternative bimorph gate of the
invention.
FIG. 19 is a perspective view of an assembly template used in an
alternative embodiment of the invention.
FIG. 20 is the bimorph gate of FIG. 18 after assembly.
FIG. 21 is a top view of a bimorph gate of FIG. 20.
FIG. 22 is a top view of a bimorph gate array of the invention.
FIG. 23 is an enlarged view of the lower left corner of FIG.
22.
FIG. 24 is a front elevation of a bimorph gate array of the
invention.
FIG. 25 is an enlarged view of the lower left corner of FIG.
24.
FIG. 26 is a diagram of the source optics for the invention.
FIG. 27 shows one embodiment of a filter tray for the
invention.
FIG. 28 shows another embodiment for the filter tray of the
invention.
FIG. 29 shows an alternative embodiment for the source optics of
the invention.
FIG. 30 shows an alternative embodiment for the filter tray of the
invention.
FIG. 31 shows an alternative embodiment of the invention utilizing
the filter tray of FIG. 30.
FIG. 32 is a block diagram showing the entire system of the
invention. entire system of the invention.
FIG. 33 is a representation of an array of shelves utilizing the
bimorph gates of the invention.
FIG. 34 is a partial schematic view of the optical fiber
connections of the invention.
FIG. 35 is a partial elevation of two bimorph gate shelves of the
invention.
FIG. 36 is a partial elevation of four bimorph gate shelves of the
invention.
FIG. 37 is an elevation of an alternative embodiment of the
invention.
FIG. 38 is an enlarged exploded view of a portion of FIG. 37.
FIG. 39 is an exploded sectional view taken along the line 39--39
of FIG. 37.
FIG. 40 is an "X-ray" view of a portion of a top printed circuit
board of the invention.
FIG. 41 is a top view of a portion of a bottom printed circuit
board of the invention.
FIG. 42 is an "X-ray" view of an alternative top printed circuit
board of the invention.
FIG. 43 is an "X-ray" view of a portion of another alternative top
printed circuit board of the invention.
FIG. 44 is a side view of a portion of the embodiment of the
invention shown in FIG. 43.
FIG. 45 is a block diagram of an alternative embodiment of the
invention.
FIG. 46 shows photographic masks for use in connection with making
the embodiment of FIG. 45.
FIG. 47 shows a filter for use in connection with the embodiment of
FIG. 45.
FIG. 48 shows a bimorph shelf for use in connection with embodiment
of FIG. 45.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. 1, there is shown a perspective view of one
embodiment of a bimorph light modulator according to the teachings
of the invention. An input fiber optic light guide 20 is glued to
the underside of an input fiber holder 21. In the preferred
embodiment, the fiber holder 21 is 2-mil brass shimstock, and the
input optical fiber 20 is glued thereto using an epoxy glue. In the
preferred embodiment, the input fiber optic light guide 20 is 250
microns in diameter. An output light guide 22 is registered center
line to center line with the input light guide 20. In the preferred
embodiment, the output light guide 22 can be optical fiber or a
bundle of optical fibers having a diameter of 750 microns. The
output light guide 22 may be fastened to a substrate 23 in any
known manner. The input light guide 20 rests on an extension of the
substrate 23. The substrate 23 can be 1-2 millimeter (mm) brass
plate or 2-3 mm plastic. In general, it is preferred to keep all
dimensions of thickness as small as possible so that the maximum
number of pixels may be obtained in the Z direction. The gap
between the input fiber holder 21 and the substrate extension 25
may be left filled with air, or it may be filled with a pliable
insulating material such as rubber or potting compound to provide
an additional degree of mechanical support.
The input light guide 20 and the output light guide 22 are
separated by a gap indicated generally at 24. A shutter 26 is
placed in the gap 24 and is mechanically affixed to a bimorph 28.
The bimorph 28 flexes in accordance with the intensity and duty
cycle of electrical fields applied via a high voltage conductor 30,
a high voltage center electrode 31 and ground connections (not
shown). When a high voltage of a proper polarity is applied, the
bimorph 28 bends upward, i.e., in the positive Z position, thereby
removing the shutter 26 from the gap 24. This permits light in the
input light guide to be captured by the output light guide 22 and
guided to the pixel location controlled by this particular bimorph
light modulator.
In the preferred embodiment, pulse width modulation is used for the
high voltage control signal on the electrode 31, thereby causing
the shutter 26 to move into and out of the gap 24 with a duty cycle
controlled by the pulse width parameter. The duty cycle controls
how much of the time the shutter 26 is in gap 24 and completely
occluding light transfer from the input light guide 20 to the
output light guide 22. The higher the percentage of time that the
shutter 26 is in the gap 24 and occluding light flow, the lower is
the average light flux transferred from the input light guide 20 to
the output light guide 22. This lower average light flux will be
perceived by the human eye by virtue of the eye's natural averaging
process as a lower light intensity emerging from the pixel
controlled by the bimorph light modulator of FIG. 1.
The electrical fields needed to operate the bimorph 28 require both
a high voltage source and a ground plane as well as metalized or
conducting surfaces on the bimorph structure to cause the
electrical field to pass through the piezo film. As will become
clear from the discussion below, the ground plane must be connected
to the metalized films on two surfaces of the bimorph on opposite
sides of the metalized film used for the high voltage. The manner
in which this is done will be made clear in the discussion below.
The ground plane in the embodiment of FIG. 1 is the conductive
plate 32. The high voltage electrical lead 30 is insulated from the
conductive plate 32 by a layer of insulating material (not shown)
so as to prevent a short between these two conductors of differing
potential. One ground connection is to a metalized film on the
underside of the bimorph 28. Another ground connection is to a
metalized film on the top of the bimorph 28 (not shown). The exact
manner of one embodiment of electrical connections is shown in FIG.
11.
Obviously, the color of the light conducted into the bimorph light
modulator by the input light guide 20 is not important so long as
the input guide light 20 is capable of guiding that frequency of
light. Thus the bimorph light modulator of FIG. 1 can be used for
implementing color displays by grouping three bimorph light
modulators and three input light guides together as a single pixel
where each light modulator controls the intensity of one of the
three primary colors. Because fiber optic light guides are used in
the preferred embodiment, distributed pixels are also possible. In
such an arrangement the output fiber or output fiber bundle 22 is
distributed in a pattern over a local matrix of red, green and blue
pixel positions. In such an embodiment, the pixel positions may
overlap each other in the matrix to provide a smoother appearing
display.
Referring to FIG. 2 there is shown the preferred embodiment of a
bimorph light modulator according to the teachings of the
invention. The light modulator is built on a substrate comprised of
either 1-2 mm brass or 2-3 mm plastic. The substrate 23 provides
mechanical rigidity for the superstructure built thereon. The input
light guide 20 rests on the top surface of the substrate 23 but is
mechanically affixed to a brass shim plate 21 which is 0.002 inches
thick (2 mil) in the preferred embodiment. The input light guide 20
extends from the rear edge of the board 31 to the front edge 29 of
the board. As with the embodiment of FIG. 1, the input light guide
20 is optical fiber of a diameter of 250 microns, and is glued to
the brass plate 21, but other forms of affixation will also
work.
The next layer up from the brass plate 21 is a printed circuit
board 27. This printed circuit board does not extend all the way to
the front edge 29 of the bimorph light modulator. Instead, the
printed circuit board 27 extends from the rear edge 31A to a
position along the X axis just short of the bimorph fulcrum 33. The
portion of the printed circuit board 27 closest to the fulcrum is
used to make the electrical ground plane connection to the bimorph
28. That is, standard copper traces may be formed on the surface of
the printed circuit board 27 facing the underside of the bimorph 28
such that the bimorph may be glued to these electrical traces using
conductive epoxy to both form an electrical connection and a
mechanical mount. The details of the electrical connection scheme
will be clarified in connection with the discussion of FIG. 11. The
mechanical attachment of the bimorph is by way of the electrical
connections to the printed circuit board 27. The electrical
connections are covered by a pliable insulating layer such as
rubber or potting compound 35.
The advantage of using the printed circuit board 27 is that the
connections to the bimorphs may be made by standard copper
conductive leads etched onto the surface of the printed circuit
board. Further, integrated circuit sockets and conductive traces
leading up to each pin connection point may be formed in the
printed circuit board such that the driver circuitry for whatever
modulation scheme which is chosen by the user may be built on the
printed circuit board.
A brass spacer 37 rests on top of the printed circuit board 27 to
provide mechanical support and spacing for a top plate 39. The
purpose for the top plate 39 is to shelter the bimorph 28 and to
provide mechanical support for a top stop 41. The purpose of the
top stop 41 is to limit the upward movement of the bimorph shutter
end and to damp any resonant vibrations of the bimorph cantilevered
beam. The damping is to limit the movement of the bimorph to a
range which is adequate to cause the shutter 26 to be completely
removed from all possible light paths from the input light guide 20
to the output light guide 22 (not shown). The bimorph vibrations,
if not damped, could cause the shutter 26 to oscillate up and down
in the Z direction each time the bimorph 28 is relaxed to place the
shutter 26 in front of the input light guide 20, i.e., in the off
position. These vibrations could cause the shutter 26 to move in
and out of the light path when it is supposed to be solidly in the
light path and completely occluding light transfer from input to
output. Such vibrations are a cause of error in controlling the
intensity of light by a cantilevered beam bimorph and destroy the
repeatability of the result.
The top and bottom stops could be knife edge stops. In such an
alternative embodiment, the voltage driving signal can be reversed
just before contact of said bimorph with either stop to decelerate
the bimorph and eliminate the bounce which would otherwise occur
when the bimorph hits the stop, where no viscous damping is present
because of the narrow nature of the top and bottom stops.
To improve the speed with which the bimorph opens and closes, the
bimorph is "overdriven" in the sense that the amount of voltage
applied is much greater than the amount of voltage needed to move
the bimorph between the top and bottom stops. This reduces the rise
and fall times of the operation of the gate in moving from an open
to closed position, and vice versa, as would be seen if shutter
position as a function of time were plotted at the voltages used in
the invention versus lower voltage driving signals.
Conductive traces 43 and 45 shown in FIG. 2 represent high voltage
signal lines to adjacent bimorphs. The structure shown in FIG. 2 is
typically built with 16 bimorphs side by side, such that 16 pixels
in black and white displays may be controlled with the structure of
FIG. 2. When these structures are stacked, a twodimensional array
may be formed.
Referring to FIG. 3, there is shown a perspective, exploded view of
a typical bimorph construction. A bimorph is a laminated structure
using a class of polymers that exhibits piezoelectric properties.
The most common polymer of this class of materials is
poly(vinylidene fluoride).sub.2, sometimes referred to as PVF.sub.2
or PVDF. This class of polymers can be manufactured in such a way
that the molecular structure is aligned. Then the structure is
poled in an intense electric field to effect separation of charges
resulting in an electric material which exhibits piezoelectric
properties and electrostrictive properties. Piezoelectricity is the
property that when a material is subjected to mechanical stress, it
generates a voltage. Electrostrictive effect is the opposite; when
the material is subjected to an electric field, the material
changes dimensions. The manufacture of such films is a well known
process, and it is commercially available under the trademark
Kynar.TM. from Pennwalt Corporation in Philadelphia, Pa. Such films
come with metalization coatings on the surfaces which can be used
to apply the electric fields by applying voltages to these
metalization films. A strip of PVF.sub.2 will lengthen (or shorten)
by a fractional amount that increases with voltage and decreases
with film thickness.
Bimorphs are constructed by fastening two such films together in
such a way that the electric field across each is arranged to
contract one layer and elongate the other. This bimorph
construction will be sometimes referred to herein as a bimorph beam
or a beam. With one end of the beam held fixed and a voltage
applied, the free tip of the beam will undergo an excursion or tip
deflection. With a shutter such as the shutter 26 in FIG. 1
attached to the free end of the beam, this tip deflection allows a
bimorph gate to open or close a light path, thereby allowing light
coupling and decoupling between an input light guide and an output
light guide.
Although bimorph beams are not new, the structure of the light
modulator described herein is new in that the bimorph is
constructed using very thin films with the resonance and chatter
problems reported by earlier investigators eliminated and with a
very accurate registration of the position of the shutter end of
the bimorph to the light path in a way to eliminate any unintended
stresses in the beam so that all bimorphs act similarly to the same
signal. Further, the bimorph is easier to construct, more reliable
and less susceptible to shorting. The bimorph light modulator uses
fiber optic light guides so certain advantages are achieved. First,
the fibers can be grouped into bundles so a single light source may
be used to supply input light to all bimorphs. This light can be
guided to pixel positions in a very large display since the fibers
are flexible. This eliminates the complexities of trying to do the
same thing with discrete, classical optics. Only one input fiber is
needed for each gate, but multiple output fibers can be used for
each gate.
The construction details of the bimorph cantilevered beam are as
follows. The bimorph is made of two strips 34 and 36 of
piezoelectric film. In the preferred embodiment, these film strips
are 9 microns in thickness along the Z axis. The two films 34 and
36 are laminated together by a glue layer 38 to form a laminated
beam construction. In the preferred embodiment, the thickness of
the glue layer is approximately one half the film thickness or less
than 5 microns. The four surfaces of the two piezoelectric film
strips are labeled S1, S2, S3 and S4 in FIG. 3. These same surface
numbers are used in FIG. 4, which shows the metalization patterns
which are formed on each surface. The glue layer 38 extends from
the edge of surface S2 to the end of the bimorph having the most
positive Y axis coordinate. This most positive Y axis coordinate
end of the beam will become the end on which the shutter is
attached later in the process of manufacturing the light modulator.
The glue layer 38 covers all of surface S2 and the portion of
surface S3 which is covered by the surface S2 in the final
construction. The particular glue used should have approximately
the same stiffness or Young's modulus when set as the piezo film
itself. Further, the glue should set in ultraviolet light in the
preferred embodiment.
Although it is possible to use epoxy glue or other glues, such
glues are not preferred since they give a limited amount of time to
work with the films after the glue is applied and before the glue
sets. It is desirable to be able to slide one film on top of the
other so as to precisely register the two film strips with relation
to each other before the glue sets. Further, it is desirable to not
have any wrinkles, bubbles, or other discontinuities in the surface
after the glue has set. Therefore, it is convenient to have a glue
which sets in ultraviolet light so that the construction of the
bimorph may proceed in an unhurried fashion and so that wrinkles
and bubbles may be eliminated from the laminate before the glue
sets. With ultraviolet setting glue, all steps of the construction
process may be carried out at leisure, and when completed, the glue
may be set by exposing the structure to ultraviolet light.
It is important to get a uniform thickness for the glue layer, and
it is important to be able to control the thickness of the glue
layer so that the glue layer is as thin as possible. Thick glue
layers cause the bimorph beam to be overly stiff. This excessive
stiffness will limit the range of deflection of the shutter when
voltage is applied. It is necessary that the bimorph be flexible
and mobile enough to completely remove the shutter from the light
path. In the preferred embodiment, the glue used is NOA-81
manufactured by Norland Optical Products.
A key factor in determining the glue thickness is how much force is
applied during the step of setting the glue. The process of gluing
the two film strips 34 and 36 together is as follows. This process
will be described with reference to FIG. 5, which is a flow chart
of the steps in the process. The first step is symbolized by block
51, which represents the process of laying out a sheet of the
piezoelectric film which will become, after dicing, a plurality of
the bottom strips 34. This sheet has the metalization patterns for
surfaces S3 and S4 formed on it--as shown in side-by-side
relationship in FIG. 4--with the surface S3 patterns on the top
side of the film, and the surface S4 patterns formed on the
underside of the film in registration with the S3 surface
patterns.
The long dimension of the metalization patterns is formed
coincident with the access of highest electrostrictive sensitivity.
That is, in the process in which the film is manufactured, the
piezoelectric properties are introduced into the sheets of film by
a process known as poling. In this process a strong electric field
is applied across the thickness of the film at 110.degree. C. to
align the polymers into polarized chains. This produces polarized
film with a positive and a negative side. The extrusion process
also introduces an asymmetry into the film. This means that the
polymer chains, in addition to being polarized through the
thickness of the piezo film, are stretched in the direction of
extrusion, and this direction becomes the direction of the highest
piezoelectric or electrostrictive sensitivity. This direction is
also the direction chosen for the longitudinal axis of the
metalization patterns.
As indicated by step 51, the bottom sheet of piezo film is laid
upon a glue resistant surface. In the preferred embodiment, as it
is presently known, the bottom sheet is laid upon a heavy glass
plate with a film of Saran wrap or other glue resistant film
interposed between the piezo film and the glass surface. In other
embodiments, the glue resistant surface may be Teflon or some
sprayed material. The purpose of the glue resistant surface is to
prevent the bimorph from becoming glued to the glass plate during
the process of setting the glue. Ultimately the bimorph laminated
construction is to be squeezed between two glass plates so as to
make the glue layer 38 as thin as possible. This squeezing process
squeezes the glue out from between the two piezo film sheets. This
excess glue can glue the bimorphs to the glass if the glass
surfaces are not made glue resistant.
The next step is to eliminate wrinkles in the bottom film as
symbolized by step 53. Because the piezo films are so thin, they
exhibit a natural curl resulting from the process by which they are
made and are somewhat difficult to work with. Steps must be taken
to eliminate this curl. One of these steps is annealing the film
after metalization by temperature cycling it between 20.degree. C.
and 70.degree. C. several times. Any remaining curl after this
annealing process should be eliminated prior to laminating the two
films together so as to produce as straight a bimorph as possible.
Thus some step must be taken when laying the bottom sheet on the
glass plate to eliminate any curl which would cause the film to not
lie flat on the glass surface. One way of doing this is to spray
the glass surface with a wetting agent which evaporates such as
Windex and then to lay the piezo film on the glass in contact with
the wetting agent. The wetting agent tends to make the thin film
stick to the flat glass surface and lie flat upon it. The film can
then be freely slid across the surface to register it with
registration marks. These registration marks insure that the film
is in the proper location for lamination with the top film. This
registration is necessary because the top film will be brought into
contact with the bottom layer of film using a jig having guide
means for a top plate to which the top film is attached by wetting
agent or some other means. Typically, the glass plate upon which
the bottom film is placed is registered in a fixed position by a
jig or other alignment means. The registering of the bottom film to
registration marks on the bottom glass plate is only necessary for
automated manufacturing processes where a machine will lower the
top film onto the bottom film. If hand placement is being used,
this registration may be omitted since the operator may visually
align the top film with the bottom film to achieve the alignment
shown in FIG. 3. Note that the top film 36 is shorter than the
bottom film 34 in FIG. 3 and that the top film is aligned with the
bottom film such that the shutter ends coincide. This leaves the
opposite end of the top film 36 short by the difference in film
lengths from aligning with the end of the film strip 34 opposite
the shutter. This allows space for an electrical connection to the
metalization pattern on surface S3.
Alternative ways of eliminating wrinkles would be electrostatic
charging of a conductive pattern on the bottom glass plate with
opposite charging of the metalization pattern on the bottom film so
as to cause the two surfaces to cling together electrostatically.
Another way of eliminating wrinkles would be to use a suction plate
having tiny openings in the surface thereof instead of the glass
plate. The tiny openings in the flat surface of the suction plate
would be coupled to a vacuum manifold such that the bottom film
could be maintained in flat relationship to the suction plate by
application of vacuum to the vacuum manifold.
If the Windex or wetting agent method is used, the wrinkles may be
eliminated by rolling the film onto the flat surface using a
roller. This process eliminates wrinkles and does not induce
stresses in the film which could be produced by stretching the film
to eliminate the wrinkles. It is important not to induce stresses
in the films because such stresses will result in curled or twisted
bimorphs after cutting.
The next step is to apply the glue to the surface S3 of the bottom
film 34. Preferably, this glue application process will be by some
method which does not induce stresses in the bottom film 34.
Preferably, the glue is sprayed on, but it may also be dabbed on
gently. Alternatively, the glue may be applied to the top film 36
on the surface that will face the bottom film 34.
Next, the top piezo film 36 is placed on glue resistant surface
number 2 as symbolized by block 57. Typically, this glue resistant
surface is a glass plate with plastic film or some other glue
resistant coating between the piezo film and the glass. This
process is the same as the process described with reference to step
51. Next, step 59 is performed to eliminate the wrinkles and
register the top sheet with alignment marks on the glue resistant
surface number 2. The process of step 59 is the same as the process
of step 53.
An alternative method to steps 57 and 59 is to hand register the
top sheet with the bottom sheet of piezo film. Since, in the
preferred embodiment, the glue is UV setting, this hand
registration process can be formed at a leisurely pace to insure
that the registration is proper and that no wrinkles exist in the
final laminated structure prior to the application of ultraviolet
light. The preferred method of construction of the bimorph beam,
however, is automated.
The next step in this process of automated construction of the
bimorph beam is to bring the glue resistant surface number 2
straight down onto glue resistant surface number 1 in aligned
relationship to mate the metalized patterns as shown in FIGS. 3 and
4. In the preferred embodiment, this is done with a machine.
However, it may also be done by hand in a jig where the top and
bottom glue resistant surfaces are glass plates having glue
resistant coatings thereon. These two glass plates are of the same
size and may be registered with corner registration guides such
that the top glass plate may be lowered gently down upon the bottom
glass plate in registered alignment with the corner alignment
guides. The ultimate goal is to achieve the alignment shown in FIG.
3, and any method of achieving this alignment will suffice for
purposes of practicing the invention.
Next, clamping to get the proper glue thickness must be performed
as symbolized by step 63 in FIG. 5. There, surface 1 and surface 2
of the top and bottom pressure plates are clamped together with
sufficient force, evenly applied over the surfaces, to squeeze the
piezo films together sufficiently to achieve the desired glue layer
thickness for layer 38 in FIG. 3. The glue layer thickness is a
function of the amount of force applied. This amount of force will
have to be experimentally determined by the user. Step 63 is the
last step if the glue used is a nonultraviolet setting glue.
If the glue used is an ultraviolet setting glue, then the final
step in the process is step 65 where the clamped structure is
exposed to ultraviolet light for a sufficient time to set the glue.
In the preferred embodiment, the time needed is approximately two
hours using a standard 15 watt black light. The relative long time
to set the glue is caused by the existence of the metalization film
on the surfaces S1 and S4. This metalization filters out large
amounts of the ultraviolet light thereby slowing the process of
setting of the glue layer 38 between these two surfaces. Further,
if ultraviolet setting glue is used, the glass pressure plates and
glue resistant films used should be of materials which do not block
the particular ultraviolet light wavelengths needed to set the
glue. Further, the clamps used should not be placed in a location
which would block the passage of ultraviolet light to the glue
layer 38.
Referring to FIG. 4, more detail on the metalization patterns is
shown. The four rectangular figures in FIG. 4 represent the four
surfaces S1 through S4 shown for the bimorph laminate of FIG. 3.
The metalization patterns in the preferred embodiment are sputtered
gold with a thickness of 350 angstroms. Other metalization
materials may be used, such as copper, provided that the
metalization material will form a good bond with the particular
type of electrical connection material chosen. In the preferred
embodiment, this electrical connection material is conductive
epoxy, but in alternative embodiments, a low temperature eutectic
such as a mixture of bismuth and indium is used to sweat small
copper pads approximately two millimeters on a side to the
metalization pattern. Prior to soldering the copper pads onto the
metalization patterns, fine wires are soldered to the copper pads
using high temperature solder. The bimorph beams are extremely
sensitive to high temperatures, and can be destroyed by being
subjected to temperatures greater than 70.degree.-80.degree. C.
either during the construction process or during operation.
Further, the bimorphs exhibit undesirable thermal curl which causes
them to distort at high temperatures unless the thermal curl can be
completely eliminated by the annealing process described above.
In FIG. 4, the metalization pattern is shown as an unhatched area,
and the unmetalized film is shown as a hatched area. For example,
on surface S4, an unmetalized area 46 is shown which corresponds
generally to the size and location of the high voltage connection
pad 48 on surface S3. The purpose of the unmetalized portion 46 on
surface S4 is to eliminate the electrostrictive action of the film
in this region by eliminating the ground plane contact in this
region. The metalization pattern in S3 is the high voltage
electrode whereas the metalization pattern on surface S4 is the
ground electrode. Electrostrictive behavior of the bottom film
strip 34 is induced by charging the metalization pattern on surface
S3 to a high voltage of approximately 200 volts. The surface S4 is
connected to ground potential so that a high strength electric
field passes through the bottom piezo film 34. Because there is no
ground plane contact lying under the high voltage contact pad area
48, no electrostrictive behavior occurs in this region. The purpose
of eliminating electrostrictive behavior in the vicinity of the
high voltage contact pad 48 is to improve the lifetime, reliability
and mechanical integrity in general of the high voltage contact in
the area 48. If the dimensions of the surface of the area 48 were
changing under the electrical contact, the integrity of that
contact would be compromised, and the contact could eventually
fail.
The unmetalized region around the edges of surface S3 is present to
improve the electrical integrity of the high voltage contact in
preventing shorts between the high voltage metalization pattern on
surface S3 and the ground plane connected to the metalization
pattern on the surface S4. Since the piezo film 34 is only 9
microns thick, if the etched-back region on surface S3 were not
present, only 9 microns of polymer film would exist between the
high voltage contact and the ground plane. This could cause shorts
between the high voltage contact and the ground plane if dirt, glue
or other contaminating materials caused a bridge between the ground
plane and the high voltage electrode. The unmetalized region around
the edges of the surface S3 minimizes this possibility. Further,
this unmetalized region also reduces the possibility of
electrostatic pinning caused by edge fields. If the metalization
pattern on surface S3 were to extend all the way to the edges, an
electrical field between the high voltage electrode and the ground
plane 9 microns away would exist in the edge space around the edges
of the bottom piezo film 34. Because opposite charges attract by
electrostatic force, and the ground plane could be considered an
opposite charge, there would be an electrostatic attraction caused
by the edge field. The force exerted by this edge field attraction
could make it more difficult for the bimorph to lift itself up and
away from the ground plane when the shutter is to be withdrawn from
the light path.
The surface S2 is unmetalized in the preferred embodiment since it
is only necessary to generate an electric field through the top
piezo film 36. This is accomplished by the presence of the
metalization pattern on the surface S3 and the ground plane
metalization pattern on the surface S1 of the top sheet 36. In
alternative embodiments, the surface S2 could be metalized in a
similar fashion to the surface S3 if an electrical connection for
high voltage could be made to this surface. This could be a
preferable construction because it would cause the intensity of the
electric field through the piezo film 36 to be the same as the
intensity of the electric field through the piezo film 34. As the
bimorph is presently constructed, the electric field through the
piezo film 36 is somewhat attenuated by the presence of an
additional 5 microns of spacing between the high voltage electrode
and the S1 surface ground plane electrode caused by the presence of
the glue layer 38. However, the inconvenience of making an
electrical contact to a metalization pattern on the surface S2 is
judged to far outweigh the advantage of having the electric field
intensities identical in the films 34 and 36. One way of making
this electrical connection is to use conductive epoxy to bond the
two piezo films together to form the bimorph.
The unmetalized region 50 on the surface S1 is intended to prevent
shorts between the ground plane electrode on the surface S1 and the
high voltage electrode on the surface S3. The edge 52 of the top
strip 36 will coincide with the dotted line of the high voltage pad
boundary shown on the surface S3. This is because only 9 microns of
piezo film would otherwise separate the high voltage electrode from
the top ground plane electrode, and shorts could easily occur if
dust, glue or other contaminating materials happen to
simultaneously contact the two electrodes.
In the preferred embodiment, the metalization pattern shown in FIG.
4 is formed by sputtering gold onto the piezo film. However, the
sputtering process for gold causes high temperature due to the
energy needed to sputter the heavy gold atoms off the target. Thus,
in alternative embodiments, other metalization patterns may be
used--such as copper, since lower energies can be used to sputter
copper. Aluminum will not work, however, since it is too difficult
to bond to aluminum through the aluminum oxide unless some steps
are taken to eliminate the oxide.
There is a very high current density at the locations of the
electrical connections. If the electrical connection is not of a
low resistivity, failure can occur caused by heating in the area of
the contacts, arcing or other such phenomena. It is important,
however, that the metalization pattern have low resistance and be
free of pinholes, stretches and other defects which could raise the
resistance at the area of the defect. The reason for this is that
high current densities will exist in the metalization films during
changes of voltage levels during normal operation. The gold films
separated by insulating material together comprise a capacitor.
This capacitor is being driven by fast rise time, square-wave high
voltage signals to get rapid turn-on and turn-off times. Each time
the high voltage changes voltage level, a high current density
results as the capacitor charges or discharges. If a localized
defect raises the resistance in a particular area, arcing can occur
in that area. This arcing can eventually cause the defect to become
an open circuit thereby destroying the utility of the bimorph.
The unmetalized portions of the surfaces S1 through S4 can be
achieved either by etching or by masking during the metalization
process. An alternative embodiment is to blow the gold off the
bimorph edges in the areas to be unmetalized using a ultraviolet
light laser. Because the process of etching the gold film using
standard photolithographic techniques is messy, somewhat inaccurate
and slow, and because it creates waste disposal problems for the
used etchants, it is preferred to use masking techniques during the
metalization process. In such a process, the unmetalized areas are
masked off using standard photolithographic and masking techniques
prior to the sputtering of the metal coating. When the masking
material is removed, the desired metalized and unmetalized areas
for each bimorph surface will be defined. The etching process works
perfectly well, however, and the accuracy of the etching need not
be very high. An RMS variation of edge straightness on the order of
25 microns is acceptable.
Referring to FIG. 6, there is shown the bimorph light modulator in
a side view at a point in the process of constructing the light
modulator after registration has been completed. The mounting and
registration process is important, because it eliminates
prestresses in the bimorph cantilevered beam and insures that the
off state of the bimorph will be in a position such that the
shutter 26 completely blocks all light paths from the input light
guide 20 to the output light guide 22.
There are four requirements for the mounting and registration
process. First, the attachment must be secure and long-lived.
Second, the shutter end of the bimorph should be registered such
that the lowest tip of the shutter, i.e., the point on the shutter
having the lowest Z axis coordinate, should be registered to within
25 microns of the point on the perimeter of the input fiber 20
having the lowest Z coordinate. Further, the shutter 26 should be
registered to within 25 microns along the X axis from the output
end of the input light guide 20. The bottom edge of the shutter
must be below the lowest edge of the input fiber with a minimum
overhang of 50 microns. The third requirement of the registration
and mounting process is that the bimorph should make a small angle
with the substrate surface 21 in order to beneficially use the
viscous damping effect of the air advantageously to damp resonance
and chatter while simultaneously avoiding or lessening the effect
of hydrostatic sticking of the bimorph to the surface 21 of the
substrate. This hydrostatic sticking would occur if the bimorph
were allowed to come into contact with the surface 21 along the
whole length of the bimorph. A further requirement of the mounting
process is that when the bimorph is registered, no stresses should
exist in the bimorph other than those intended to be there, and all
bimorphs should have the same level of prestress.
FIG. 7 is a flow diagram of the process of mounting and registering
the bimorph which achieves the above-stated objectives. With
concurrent reference to FIGS. 7 and 6, this process will now be
explained. The first step is represented by block 67 where a
hemispherical fulcrum 69 is glued to the bimorph. The size of the
fulcrum and the location where it is attached to the bimorph are
selected so that the bimorph makes a shallow angle with the top
surface 21 of the input light guide holder 47, which may be brass
shim stock. Typically this shallow angle is about 5.degree., but
other angles will work. The purpose of this shallow angle is to
allow the air to be used for cushioning or viscous damping of the
landing of the bimorph on the edge 60 of the input light guide
holder 47 when the shutter 26 is lowered into the gap 24. Because
the bimorph 28 is approximately 3-4 mm wide, and is very light, the
air between the bimorph 28 and the surface 21 tends to cushion the
landing of the bimorph on the edge 60 as the air "mushes" out of
the way when the bimorph 28 is landing. This damping effect tends
to reduce the bounce of the bimorph 28 up and away from the edge 60
in the positive Z direction which would occur if the bimorph 28
were to land on the edge 60 in a vacuum. Further, the damping
effect of the air tends to minimize resonance vibration which will
occur if the natural mechanical resonance of the cantilevered beam
is excited by the driving signal. Such bounce and resonant
vibration will destroy the reproducibility of the bimorph response
to a given driving signal since the chatter and resonance tends to
alter the amount of light flux coupled between the input light
guide 20 and the output light guide 22 and because the bounce and
resonant vibration may not be the same each time the same input
signal is applied.
The shallow angle also minimizes the hydrostatic "pinning" effect
which would otherwise occur if the bimorph 28 were allowed to lie
flat on the surface 21. The reader can visualize this hydrostatic
sticking effect by trying to pick up a piece of paper by its edge
which is lying flat on a glass surface. This hydrostatic effect is
caused by the evacuation of much of the air between the bimorph 28
and the surface 21 when the bimorph 28 is allowed to settle flat
onto the surface 21. When an attempt is made to raise the bimorph
away from the surface 21, a temporarily lower air pressure would
exist in the space between the bimorph and the surface 21 until air
can rush in from the sides to equalize the pressure. During the
time when the air is rushing in from the side before the air
pressure on the top and bottom of the bimorph is equalized, there
exists a pressure differential. This differential exists because
there is higher air pressure on top of the bimorph than underneath
it. This pressure differential tends to resist movement of the
bimorph 28 up and away from the surface 21. By establishing the
fulcrum 69 so that the shallow angle is formed between the bimorph
28 and the surface 21, evacuation of air from the space
therebetween is eliminated so that the hydrostatic pinning effect
cannot occur. The proper shallow angle is achieved by using a
hemispherical fulcrum which has a diameter of 1.5 mm and which is
located at the proper point on the bimorph to establish the
angle.
The point of attachment of the fulcrum to the bimorph is also
selected to be left of the center of gravity of the bimorph such
that the shutter end to the right of the fulcrum 69 in FIG. 6 is
heavier than the portion of the bimorph to the left of the fulcrum.
This imbalance aids in the registration process as will become
clear from the discussion below.
These substeps in gluing the fulcrum to the bimorph symbolized by
step 67 in FIG. 7 are shown to the right of the block 67 in FIG. 7
as indicated by the dashed leader line 71. The first substep is
step 73 wherein a layer of glue of the proper thickness is
established. The proper thickness may be experimentally determined
with the criterion being that the amount of glue used to glue the
fulcrum to the bimorph should not be so excessive that it becomes
enough to cover the fulcrum and should not be so little as to
render the attachment of the fulcrum not mechanically secure. A
good way of establishing the proper thickness for the glue layer is
to fasten two metal shims or strips of the desired glue layer
thickness to a glass substrate and then fill the slot between the
two shims with glue. A squeegee or other straight edge may then be
dragged over the top of the two strips leaving a layer of glue of
the desired thickness between the two strips.
The next substep is step 75, wherein a dab of the glue from the
glue layer made in substep 73 is picked up using a pickup tool. The
desired thickness of the glue drop so picked up will be established
by the thickness of the layer of glue established in substep 73
while the diameter of the drop will be established by the diameter
of the tip of the pickup tool. Typically, the pickup tool is a
small truncated cone with the truncation at the tip of the cone at
the point of the desired diameter for the glue drop. The pickup
tool is simply lowered into the glue layer and picked up, thereby
leaving a drop of glue at the tip of the pickup tool by the
adhesion of the glue to the pickup tool tip.
The next step, symbolized by block 77, is to place the drop of glue
at the proper location on the bimorph. In the preferred embodiment,
this is accomplished by a jig. The bimorph is placed on a flat
surface of the jig and registered with registration marks. Vertical
guide assemblies are provided at locations relative to these
registration marks such that the pickup tool may be slid down these
vertical guides in such a manner that the tip of the pickup tool
will land on the bimorph at the precise location where the fulcrum
is to be attached. The drop of glue on the tip of the pickup tool
will then be deposited at the proper location on the bimorph.
Next, a fulcrum is picked up by a fulcrum placement tool. In the
preferred embodiment, the fulcrum is picked up by a vacuum tool
which has a tip which mates with the curved surface of the fulcrum.
The tip has a vacuum channel in it connected to a vacuum pump such
that the fulcrum may be retained on the tip by suction through
application of vacuum to the vacuum channel. Alternative methods of
picking up the fulcrum could include magnetic attraction or
electrostatic attraction.
Next the fulcrum and the pickup tool are lowered so as to place the
fulcrum in the glue drop at the proper point on the bimorph. This
step is accomplished in the preferred embodiment using the same jig
as was used to register the drop of glue at the proper location.
That is, the pickup tool is lowered down the vertical registration
guides such that the tip of the pickup tool automatically arrives
over the location of the glue drop. The fulcrum is then lowered
into the glue drop and the vacuum to the pickup tool is cut off so
that the pickup tool may be removed and the fulcrum will stay in
the glue drop. The final step is to allow the glue to set as
symbolized by block 83.
The next step in mounting the bimorph and registering it is to
place the ultraviolet setting glue drops on the surface 21. This
step is symbolized by the block 85 in FIG. 7. These glue drops will
securely mechanically attach the fulcrums 69 to the surface 21 for
the bimorphs on each particular shelf such as that shown in FIG. 2.
The glue drops are ultraviolet setting in the preferred embodiment
and are sized such that they will form a secure mechanical
attachment while not being so large as to cause difficulties in
other steps of the process. The size of the glue drops can be
controlled in a similar fashion as was done in substeps 73 and 75
previously discussed. The location of the glue drops on the surface
21 can be accomplished in a similar fashion as discussed above with
reference to step 77. A different jig may be used in which the
structure of FIG. 6 is registered such that the vertical guides
will correctly position the glue drops on the surface 21. It is
also possible to use the same jig as was used to glue the fulcrums
to the bimorphs and to use the same vertical registration
guides.
The process of attaching the shutter is to glue a strip of foil to
the shutter end of the bimorph. The length of the shutter is then
cut by registering the bimorph in a jig and using a cutting tool
registered to guides on the jig to register the cutting position of
the blade on the foil. A slight force is then applied to the
cutting tool to cut through the foil. The bimorphs are then clamped
down by another tool such as a plastic block which is registered on
the jig to clamp all or part of the bimorph on the film side of the
shutter holding edge down to a flat surface while exposing the
film. The clamping tool has a surface aligned with the shutter edge
which is perpendicular to the surface of the bimorph and defines a
plane in which the line defined by the edge of the bimorph lies. A
sponge is then used to lift the foil up and bend it at the edge of
the bimorph so as to bend the foil to lie on the perpendicular
surface defined next above. This bends the shutter to the proper
angle. This process is done before the fulcrums are lowered into
their respective glue drops.
The next step is to allow the bimorphs to free fall into contact
with the edge 60 such that the shutter 26 is in the gap 24. This
may be done by hand placement or in automated fashion. In either
process, after the fulcrums are placed in their respective glue
drops, the bimorphs are released from a position with their shutter
ends held above the bottom stop surface 60 such that the shutter
ends fall down into contact with the edge 60. A vacuum,
electrostatic or other type of tool may be used to retain the
bimorphs 28 in the position above the bottom stop until the free
fall is triggered at which time the force holding the bimorph above
the bottom stop is released so that gravity takes the bimorph down
to the bottom stop.
In the preferred embodiment, a registration tool having vacuum
ports is used to maintain the bimorphs 28 in a raised position by
suction forces prior to the free fall. This same tool is used to
hold the bimorphs in the proper position to allow the fulcrums to
be lowered into the corresponding glue drops. The bimorphs and the
tool are then lowered down vertical registration guides until the
fulcrums 69 are located in the glue drops on the surface 21. The
shutter ends 62 of the bimorphs will be in a raised position such
that the shutter 26 is not in the gap 24 at the point when the
fulcrums 69 contact the glue drops on the surface 21.
The free fall portion of the registration process is then
performed. To accomplish this in the preferred embodiment, the
vacuum is released such that the bimorphs fall into their positions
in contact with the edge 60. Because the fulcrums 69 are
hemispherical in shape and because the rounded surfaces face the
surface 21, during the free fall into registered position, any cant
of the shutter edge 62 at an angle to the Y axis may be eliminated
during the fall. To ensure that the shutter edge 62 is parallel to
the Y axis prior to setting of the glue drops on the surface 21, an
alignment tool having flexible projecting fingers 89 is used. This
tool is brought close enough to the edges 62 of the bimorph such
that one finger 89 comes into contact with each bimorph shutter
edge 62. The flexible fingers 89 are elastic but somewhat malleable
so that each finger may be aligned with the center line of the
bimorph to which it corresponds. Each finger is elastic enough to
apply a slight downward pressure in the direction of the negative Z
axis to the edge 62. Because the edge 60 is parallel to the Y axis,
the slight downward pressure will force the edge 62 to register
itself parallel to edge 60 and to the Y axis. The resultant
structure is then exposed to ultraviolet light to set the glue
drops on the surface 21, thereby mechanically securing the fulcrum
69 in registered position. These latter two steps of applying
slight downward pressure and then exposing the glue drops to
ultraviolet light are symbolized by blocks 89 and 91 in FIG. 7.
Note that the process of free fall registration allows each bimorph
to settle to a registered position without imposing stresses on the
bimorph film in the registration process itself. If such
prestresses were fixed into the bimorphs during the registration
process and the glue drops on the surface 21 were then set with
each bimorph having different prestress loads, each bimorph would
respond differently to the same input signal, i.e., each bimorph
would begin to open at a slightly different voltage. This would
cause undesirable variation from one pixel to another for a uniform
input signal. The registration process is important, as is the
elimination of as much unintended prestress as possible in the
bimorph structure so as to insure that all the bimorphs begin to
open at approximately the same voltage. That is, all the bimorphs
in a particular application should start their upward movement to
withdraw the shutter 26 from the gap 24 at approximately the same
voltage.
Some mechanical prestressing of the bimorphs is desirable, because
bimorphs exhibit a phenomenon known as elastic lag. The effect of
this property is to distort the response of the bimorph when driven
by a pulse-width modulated electrical signal. This distortion takes
the form of a D.C. bias which is introduced into the optical
response of the bimorph gate. In order to avoid this problem and to
insure repeatability in the response, mechanical prestressing of
the bimorphs is necessary.
The elastic lag which causes this problem is the result of the
properties of the bimorph film. When the bimorph is subjected to a
voltage to cause it to bend upward, the shutter 26 will be removed
from the gap 24. When this voltage is released, the bimorph
straightens out and simultaneously, the shutter end 62 begins to
fall so as to lower the shutter 26 back into the gap 24. However,
as the bimorph straightens out, it does not return in a continuous
fashion to the registered state shown in FIG. 6. Instead, the
bimorph straightens out to a point somewhere above the registered
position, i.e., some point in the positive Z direction above edge
60. From that point, the rate of descent of the bimorph changes to
a much slower rate due to the effect of elastic lag. Since this
adversely affects the amount of time needed to "close" the bimorph
such that the shutter completely occludes the light path, the
elastic lag shows up as a D.C. bias in the optical response of the
bimorph gate.
The mechanical prestressing solution to this problem is to place
shims underneath the input light guide 20 and the output light
guide 22 so as to raise both light guides and the edge 60 of the
bottom stop to a higher point on the Z axis. Alternatively, the
position of the bottom stop registration edge 60 may be raised and
the light guides left where they are if a longer shutter is used so
that the light path is completely occluded when the bimorph is
resting on the edge 60. This new point for the edge 60 is selected
to be the point where the elastic lag effect starts. Thus the
movement of the bimorph downward is stopped by the edge 60 at the
point where the elastic lag would normally take effect. In some
embodiments where the driving frequency of the bimorph gate is not
high enough to make the elastic lag a problem, these shims may be
omitted.
The shimmed structure is shown in FIG. 8 with shims 91 and 93
raising the input light guide 20 and the output light guide 22 by
an amount equal to the distance covered by the elastic lag. Thus
the top edge of the bottom stop, i.e., edge 60 is at the point
where the elastic lag starts in the downward movement of the
bimorph 28 in the negative Z direction.
Referring to FIG. 9, there is shown a side view of the bimorph
construction using a top stop. In the structure of FIG. 9, the
brass shim stock 47 in FIG. 6 is augmented by a five mil layer of
double sided foam tape 91. Prebiasing in FIG. 9 is obtained by
inserting additional shims between the fiber 20 and the tape 91
after mounting of the bimorph is done. Additional shims 93 are then
placed under the output light guide to maintain the alignment of
the light paths of the two light guides. FIG. 9 also shows an
alignment pin and hole combination 95 and 97, respectively, which
are used to align the substrate 23 supporting the bimorph to an
adjoining substrate 99, which supports the output light guide 22.
This alignment pin and hole combination insures that the center
lines of the two light guides 20 and 22 are coincident. In an
alternative embodiment, the pin/hole combination 95 and 97 are
replaced with a pair of grooves in the top surface 92 and bottom
surface 94, respectively, of the substrate 23. These grooves (not
shown) are engaged by projections (not shown) on the substrate 99
and the top piece 96 coupled to the substrate 99. These projecting
portions engage the grooves so that the "exit optics", i.e., the
substrate 99 and accompanying structures, may be plugged or
unplugged easily. After the grooves are engaged by the exit optics,
the substrate 99 may be slid along the Y axis until the centerlines
of the light guides are aligned.
FIG. 9 also shows a top stop 101. The top stop 101 is a projecting
portion of a cover piece which is mechanically affixed to a
top-printed circuit board 103. The cover 100 serves to protect the
bimorph 28 from any physical intrusions by gusts of air or physical
objects. This top stop 101 is placed in the path of movement of the
bimorph 28 to limit the maximum amount of upward movement that the
bimorph 28 may make. The top stop 101 is placed at a position on
the Z axis such that the shutter end of the bimorph 28 may move
upward in the positive Z direction only enough to remove the
shutter 26 from the gap 24, far enough to clear all light paths
from the input light guide to the output light guide. When the
bimorph 28 nears the top stop 101, any resonant ringing in the
cantilevered beam is also eliminated by viscous damping. The
positioning and size of the fulcrum 69 in FIG. 9 are as described
earlier with reference to FIG. 6, and the width of the bimorph 28
is such as to cause viscous air damping to occur to minimize bounce
or chatter when the bimorph 28 lands on the bottom stop 60. The
same viscous air damping occurs when the bimorph comes into contact
with the top stop if the top stop is at least one third the length
of the bimorph from the shutter end to the fulcrum position. The
cavity 102 is useful in that it allows clearance for any curves in
the bimorph when the bimorph is raised to a position to be in
contact with the top stop.
The printed circuit board 103 lies above the bimorph 28 on the Z
axis, and is one of a pair of printed circuit boards used in the
embodiment of FIG. 9. The other printed circuit board 107 lies
beneath the bimorph. The purpose of these two printed circuit
boards is to allow electrical connections to be made to the two
metalized surfaces which act as ground planes for the bimorph and
to the single metalized surface which acts as the high voltage
electrode of the bimorph. The ground connections to surfaces S1 and
S4 of the bimorph are shown at 104 and 105, respectively. The
ground connection 104 between the top surface S1 of the bimorph and
a metalized conductive pattern on the printed circuit board 103 may
be made by a low temperature eutectic solder or, preferably, by a
conductive epoxy. The ground connection 105 couples the metalized
pattern on the surface S4 of the bimorph to a metalized conductive
layer on the top surface of the printed circuit board 107. The
metalized conductive pattern electrically connected to the
electrical contact 104 makes contact with a ground wire in a ribbon
cable 109 which has multiple wires connected to various conductive
patterns on printed circuit boards 103 and 107. The conductive
pattern on printed circuit board 107, which is electrically
connected to the ground connection 105, also leads to a ground wire
in the ribbon cable 109 and is electrically connected thereto.
The high voltage connection to the bimorph is shown at 111. This
high voltage connection is either a low temperature eutectic
solder, such as indium/bismuth, or a dab of conductive epoxy
coupling the metalized area 48 on the surface S3 of the bimorph to
a conductive pattern formed on the underside of the printed circuit
board 103. This conductive pattern leads to and is electrically
connected to a high voltage wire in the ribbon cable 109. The
ribbon cable 109 can go to a remotely located bimorph driver
circuit in the embodiment shown in FIG. 9.
A better understanding of the manner in which the electrical
connections are made may be gained by referring to FIGS. 10 and 11.
FIG. 10 shows a side view on a larger scale of the bimorph high
voltage and ground connections, while FIG. 11 shows a top view of
the high voltage and ground connections. The particular embodiment
shown in FIGS. 10 and 11 uses a single printed circuit board 113 as
the substrate. A high voltage conductor 115 is formed on the
surface of the printed circuit board 113 as a metalized trace. A
ground conductor 117 is also formed on the surface of the printed
circuit board 113 as a metalized trace. In FIG. 11 three individual
high voltage traces 115, 119, and 120 are shown so that the
individual bimorphs 121, 123, and 125 may be individually driven
with signals indicating the light intensity to be emitted from the
pixels controlled by those particular bimorphs. A single shared
ground trace 117 is also shown. Each of the bimorphs in FIG. 11 is
both mechanically affixed to the substrate 113 and electrically
connected to the corresponding high voltage trace by a dab of
conductive epoxy, shown as glue drops 127, 129, and 131 in FIG. 11.
The metalized patterns on the surfaces S1 of the three bimorphs in
FIG. 11 are shown connected to the ground trace 117 by individual
glue drops of conductive epoxy 133, 135, 137, and 139. The surfaces
S4 on the underside of the bimorphs shown in FIG. 11 are coupled by
conductive epoxy drops 141, 143, and 145 to the shared ground trace
117. These latter glue drops are shown in phantom in FIG. 11. The
epoxy glue drops shown in FIG. 11 serve not only to make the
electrical connections but also serve as the mechanical mounting of
the nonshutter end of the bimorph to the substrate 113.
Referring to FIG. 12, there is shown one possible embodiment for a
shelf layout of sixteen adjacent bimorph electrical modulators. In
this particular embodiment, the fiber optic input light guides 20
are bundled together at the left side of the board to form an input
light bus 150. The individual input light guides then branch off to
their individual bimorphs, as shown generally at 153. An edge
connector 155 allows power, ground, and logic level signals to be
input to the board to control the light intensity modulation of
each bimorph. A 16-channel high voltage driver (not shown) is
mounted on the board generally at 157. The incoming pixel data for
each bimorph is coupled to the 16-channel high voltage driver by
one of the conductive metallic traces etched on the surface of the
shelf, which is typically a printed circuit board or other
insulating-type substrate material. Phenolic printed circuit board
is preferred, however, since techniques for forming conductive
strips on such boards are well known. The high voltage signals from
the high voltage driver to the bimorph center electrodes are then
conducted to the bimorphs by metallic conductive traces on the
printed circuit board substrate 23. The plan view of FIG. 12 is
shown without the top stop in position so as to expose the details
of the interconnections of the bimorphs to the edge connector and
the high voltage driver. The metallic trace for the ground plane
117 is also not shown in FIG. 12. The high voltage connection in
FIG. 12 is shown as a solder pad, as used in certain embodiments.
This solder pad is typically a copper plate which is soldered to
the metalized pattern for the high voltage electrode using the low
temperature eutectic bismuth/indium solder. Prior to this step, a
wire is bonded to this copper pad and to the particular high
voltage trace conductor on the surface of the printed circuit board
23, which corresponds to the light intensity signal for that
particular bimorph. In alternative embodiments, the connective
epoxy method of forming the high voltage and ground plane
connections, as shown in FIG. 11, may be used.
The preferred embodiment of the typical shelf layout uses the
conductive epoxy electrical connection structure of FIG. 11 and
also uses the lamination sequence shown in FIG. 2. This allows the
input light guide 20 for each bimorph to pass through from the
front edge 159 of the board straight back to the rear edge 161 of
the board. This eliminates the need to bend all the fibers to bring
them together at one side of the shelf as the light bus 150. Other
than these differences, the layout of the shelf is substantially
the same as shown in FIG. 12.
An electrooptic modulator module may be constructed using a
plurality of the shelves as shown in FIG. 12. Such a module is
shown in FIG. 13. In FIG. 13 a plurality of shelves, as shown in
FIG. 12, are stacked vertically in a framework with sixteen shelves
stacked vertically, each shelf containing sixteen bimorphs. The
input light guides are coupled to a tricolor light bus 160, which
contains three fiber optic light guides, each carrying feeder light
of one of the three primary colors red, green, or blue. In color
display applications, each pixel will be comprised of one red
bimorph, one green bimorph, and one blue bimorph. The relative hue
and intensity of each pixel then will be controlled by three
signals which modulate the relative intensity of each of the three
primary colors. The overall brightness level of that pixel can be
controlled by modulating the light intensity of all three colors
simultaneously by equal amounts. This is done by changing the duty
cycle of all three primary colors for that pixel simultaneously to
increase the on time or decrease the on time.
In the embodiment shown in FIG. 13, the tricolor light bus 160 is
coupled to the fiber optic bundles of light guides that run down
the left edges of the shelves constructed in accordance with the
embodiment shown in FIG. 12. If shelves of the structure shown in
FIG. 2 are used, the tricolor light bus 160 is coupled to the input
light guides 20 as they emerge from the back edges 161 of the
shelves. In some embodiments, a fiber optic edge connector will
couple the tricolor light bus to the back edges 161 so as to couple
light into the input light guides emerging from these back edges.
The edge connectors 155 couple to a plurality of buses in a back
plane surface 165. These power, ground, and logic signals in the
back plane 165 emerge from the electrooptic modulator controller
167. The purpose of this controller 167 is to convert the
brightness level and hue information for each pixel into a suitable
analog or digital signal to control the application of high voltage
to the corresponding bimorph which is modulating light for that
pixel position in the display. The particular modulation scheme
chosen depends upon the user's application. Therefore, the details
of a particular modulation-type controller will not be specified in
great detail. However, one suggested controller architecture is
shown in FIG. 14.
Referring to FIG. 14, there is shown one possible architecture for
a controller for the type of bimorph light modulator disclosed
herein. In this architecture, the desired light intensity for each
pixel, or for each color component of each pixel, arrives on the
line 169 as a digital or analog signal. In the preferred
embodiment, the magnitude of this signal in terms of either its
analog amplitude or its binary value will present the gray-scale
value of desired intensity for that pixel. This gray-scale value is
converted to a corresponding duty cycle by the converter circuitry
171. Because pulse-width modulation has been selected for this
example of a controller architecture, the converter circuitry 171
must convert the magnitude of the incoming signal on line 169 to
pulse widths having on times and off times which establish a duty
cycle which will cause an average light flux to emerge from that
pixel which will be perceived as the light intensity defined by the
signal on the line 169. There are many ways of converting the
gray-scale value to a duty cycle, and those skilled in the art will
be able to devise suitable circuitry to accomplish this
function.
The converter circuitry 171 outputs a duty cycle control signal on
a line 173. This duty cycle control signal causes a high voltage
driver circuit 175 to gate high voltage onto a line 177 during the
on time of the duty cycle control signal on the line 173, and
causes the high voltage driver 175 to block high voltage from being
applied to the line 177 during the off time of the duty cycle
control signal on the line 173. The line 177 represents the
electrical connection to the center electrode of the corresponding
bimorph. The bimorph then opens and closes the light path in the
gap 24 in accordance with the duty cycle of the high voltage on the
line 177. The input light to the bimorph in the input light guide
20 is represented by the light pathway 179 in FIG. 14. The pulses
of output light in the output light guide 22 are represented by the
line 181 in FIG. 14. Those skilled in the art will appreciate that
different forms of modulation other than pulsewidth modulation may
also be used to control the bimorph light modulator. Further, many
different architectures are possible for the controller structure
which implements the selected modulation scheme. All such
controller structures and modulation schemes which can control the
average light flux emerging from the output light guide 22 in
accordance with an input electronic signal defining the desired
pixel light intensity are intended to be included within the scope
of the claims appended hereto.
An alternative embodiment of the invention is shown in FIGS. 15-31.
The bimorph for use in this embodiment is shown as bimorph 200 in
FIGS. 15 and 16. The bimorph 200 is thicker than the bimorph 28 of
the above-discussed embodiments, with different functions and
advantages discussed below.
The bimorph 200 is formed from two layers of conventional
piezoelectric film, which are metalized on their upper and lower
longitudinal surfaces. Thus, in FIG. 15 these are layers 210 and
220, which have metallic coatings on their upper and lower
longitudinal surfaces as shown in that Figure, the coatings
comprising, for example, 5 nm thick nickel covered by 30 nm
aluminum. These metallic layers are shown as layers 230 and 240
(relative to the piezoelectric film 220) in FIG. 17.
Typically, the strips 210 and 220 will be formed from large sheets
of piezoelectric film from which they may be simply cut to form the
lengths and widths desired.
To construct the bimorph 200, a glue layer is disposed between
piezoelectric films 210 and 220, such as glue layer 250 shown in
mottled fashion in FIG. 15. The glue 250 may comprise an
ultraviolet setting glue, an epoxy, a spray-on adhesive, or other
suitable means of adhering the layers 210 and 220. Because the
piezoelectric film layers 210 and 220 are relatively thick, the
thickness of the glue layer 250 is not critical. Also, wrinkling,
bubbling and the like are less likely to occur, and a quick-setting
adhesive (such as five-minute epoxy) may be utilized. The glue 250
should be conductive, which electrically couples the opposing
metalized faces of the upper and lower films 210 and 220.
The lower layer 220 is longer than the upper layer 210 at one end
by a distance determined by the desired height of the bimorph
shutter 260, as shown on the right in FIG. 16, when the bimorph 200
is constructed. The layers 210 and 220 are adhered together, and
then the excess length of layer 220 is folded over upon itself.
With conventional piezoelectric polymer films available, if the
excess length is folded by 180.degree., a shutter of 90.degree.
(such as shutter 260) will be formed when the film partially
springs back to its original shape, as shown in FIG. 16.
The shutter 260 may be fixed firmly in position by thermal
persuasion, i.e. the application of heat to the area of the bend
270, such as by bringing into contact with the bend 270 a hot piece
of metal for a short time, or a warm piece of metal for a longer
time. Other methods (such as slitting) may be utilized to assist in
making the angle of the shutter 260 permanent.
As shown on the left in FIG. 16, the piezoelectric film 220 also
has an overlap 265 relative to the end of the layer 210 opposite
the end carrying the shutter 260. This will serve as a center
electrode tap, as will be described below.
Once the bimorph 200 is constructed as shown in FIG. 16, a bimorph
gate 280, as shown in FIGS. 18 and 20, is constructed. In this
embodiment of the invention, a gate template 290 is utilized, as
shown in FIG. 19, which greatly assists in the construction of the
gate 280 by acting as a substrate for various inserts, as will be
understood from the following discussion.
A substrate 300, as shown in FIGS. 18 and 20, is provided, which
may be any appropriate material, such as an injection molded
plastic. The substrate may be insulating or noninsulating,
according to the needs of the user. An optical fiber 310 is laid in
a groove 320 (shown in dotted fashion in FIG. 20) in the substrate
300. Then the gate template 290 is placed atop the fiber 310.
As shown in FIG. 19, the template 290 includes a groove 330
adjacent a front edge 340 thereof, and a longitudinal groove 350
extending along the length of the template 290. Within the groove
350 is formed a first ridge 360 and a second, higher ridge 370,
whose purposes will be described below. Also formed in the template
290 are transverse grooves 380 and 390. These grooves are defined
by raised areas 290A, 290B, 290C, 290D, 290E, and 290F.
The template 290 is mounted on the substrate 300 by conventional
means, such as by providing clips on the template 290 which match
recesses in the substrate 300 (not separately shown). A strip of
conductive material, such as a homogeneous conductive elastomer 400
as shown in FIGS. 18 and 20, is laid inside the transverse groove
380. It will be understood that, with a plurality of bimorph gates
280 positioned side-by-side in a gate array for use in an optical
system, the elastomer strip 400 will lay across each of the ridges
360 of the plurality of gates.
A glue bead 410 is then laid in the groove 330, and the bimorph 200
is placed into position within the groove 350, with the shutter 260
positioned in front of a forward end 420 of the optical fiber
310.
Another homogeneous conductive elastomer strip 430 is then laid in
the groove 380, on top of the bimorph 200. Thus, the conductive
strips 400 and 430 contact, respectively, the lower metalized layer
of the piezoelectric film 220 of the bimorph 200, and the upper
metalized layer of the piezoelectric layer 210. Strip 400 thus
comprises a bottom connector, and strip 430 comprises a top
connector, for the bimorph 200.
Another conductive strip 440 is laid on top of the area 265 of the
bimorph 200, which is configured to lie over the ridge 370 in the
area of the groove 390. The strip 440 is preferably a longitudinal
strip of a product known as Z-STRIP or "zebra strip," available
from Tecknit, Inc., of Cramden, N.J. This is a product which is
conductive in two dimensions, but not the third. In the
configuration of the present invention, the strip 440 is laid in
the groove 390 such that the conductive directions are horizontally
to the left and right (viewed from the point of view of FIG. 20)
and vertically, but not along the length of the strip 440 (i.e.,
into and out of the paper). This feature assists in avoiding short
circuits between the center electrode formed by the area 265 of the
bimorph 200 and the upper metalized layer of the piezoelectric film
200 of the bimorph 200.
In the preferred embodiment, the strips 400 and 430 are connected
to ground, and the strip 440 acts as a high-voltage electrode.
Alternatively, the center connection (i.e., the overlap area 265)
may be grounded, and the bottom and top connectors 400 and 430 may
be driven at -200 volts. The advantages of this arrangement are as
follows. In the bimorph array as assembled, it is preferable to
initially charge (or "pre-charge") all of the bimorphs
simultaneously, and then immediately to provide signals to the
bimorphs (by way of the connectors 400, 430 and 440) to discharge
bimorphs which should be closed and leave charged those bimorph
gates which should be opened. This happens quickly enough that the
bimorphs which are discharged do not have time to physically open
up. (The other bimorphs, however, do open up.) The pre-charge and
immediate discharge procedure requires a quick shift in the
reference (ground) voltage for the chip substrate, which may be
detrimental to the chip. Specifically, it avoids the level shifting
of the chip at 200 volts, which is used in one embodiment to make
operational a diode circuit using an intrinsic diode in the VFET to
simplify the driver circuit.
The driver circuit uses a protection diode intrinsic to each FET in
the following way. The anode of the protection diode is connected
to the FET source and the cathode of the diode is connected to the
FET drain. When -200 volts is applied to the outside electrodes
(i.e. at the bottom and the top of the bimorph), the diode is
thereby forward biased, and the bimorph, acting as a capacitor, is
pre-charged. Then the voltage is switched to 0 volts (ground), but
the charge on the bimorph remains at 200 volts until a logic signal
tells the FET itself to conduct (as the protection diode is now
reverse-biased).
Earlier circuits, instead of applying -200 volts to the outer
electrodes of the bimorph during the precharge, level shifted the
reference voltage of the chip substrate. This required using
opto-insulators which had narrow band width and complicated the
circuit. Another advantage of the present configuration is that it
avoids electrical stress on the driver chip resulting from sudden
large voltage shifts.
The bimorphs 200 are preferably placed in an array of, for
instance, 32 bimorphs, as shown in FIG. 22. The array 450 of
bimorphs may typically have the dimensions shown in FIG. 22
(expressed in mm). FIG. 23 is a top view of the lower left hand
corner of the array shown in FIG. 22, and shows the preferred
embodiment, wherein each bimorph 200 is somewhat narrower than the
channel 350 in which it lies. This facilitates the construction of
the bimorph 200.
FIGS. 24 and 25 show a front elevation of a multiple-bimorph
assembly template 460, with fibers 310 in place. In this
embodiment, the grooves 350 are preferably beveled at their sides
(as best seen in FIG. 25), which greatly assists in aligning the
bimorphs therein. The template 460 preferably has raised walls 454
and 456 for maintaining alignment of the bimorph gates 280. Beveled
areas 465 are provided at the front portion of the template 460,
and act as mounting guides for the bimorphs.
Once the desired number of bimorphs has been placed in an array as
shown in FIG. 22, a printed circuit board 470 is positioned atop
the array of bimorphs, as shown in FIGS. 18 and 20. The circuit
board 470 has a ground connection at each side (such as edge ground
connection 475), corresponding to the left and right sides from the
point of view of FIG. 22, each of which ground connections contacts
the conductive strip 430, which in turn contacts the conductive
strip 400. Thus, the strips 400 and 430 connect the grounds of the
bimorphs 200 along the entire array 450, and are grounded at the
edges of the circuit board 470.
FIG. 21 shows a top view of area of a bimorph near the front edge
340 of the template 290, once the strips 400, 430 and 440 have been
laid in place. An overlap area 480 is shown in FIG. 21, which is
where the strip 430, the bimorph 200, the strip 400 and the ridge
360 are all vertically aligned. Similarly, overlap area 490 is
where the strip 440, the bimorph 200 (in the center electrode
region 265) and the ridge 370 are vertically aligned. It will be
understood that, when the circuit board 470 is placed atop the
bimorph array 450, pressure will be localized at these areas of
overlap. This is a distinct advantage of the present embodiment,
since much less force is necessary to compress the strips by the
desired amount and to obtain good connections than if the strips
400, 430 and 440 had to make connection along their entire lengths.
Preferably, the strips 400, 430 and 440 are compressed
approximately 30%, which insures a good connection and also seals
the connections from gas and moisture, thus improving their
longevity.
The view of FIG. 21 is of the far left bimorph gate shown in FIG.
22, and thus, when the printed circuit board 470 is placed atop the
array 450, the aforementioned ground connections (such as
connection 475) on the edges of the circuit board 470 contact the
area 500 shown in FIG. 21 to make the ground connection to the
strips 400 and 430.
Once the circuit board 470 is in place, a rubber cushion 510 is
placed on top of the circuit board 470, with dimensions generally
corresponding to the dimensions of the array of bimorph gates,
generally defined by the total area of the gate template 90. Then a
top cover 520 including a front stop 530 is set in place, as shown
in FIGS. 18 and 20. The stop 430 is similar to the top stop 41
shown in FIG. 2, and is similarly designed to prevent chatter and
resonance in the bimorph 200 as it opens and closes. Thus, the
bimorph 200 will extend substantially to the position shown in
dotted fashion in FIG. 20, but not further.
Once the bimorph gate 280 is assembled as shown in FIGS. 8 and 20,
a plurality of plastic rivets 540 are inserted through coaxially
aligned holes 550, 560 and 570 in the top cover 520, the printed
circuit board 470, and the substrate 300, respectively, as shown in
FIG. 18. The bimorph gate 280 as a whole is compressed (such as in
a vise), as mentioned above, such that the strips 400, 430 and 440
are compressed approximately 30%, and the rivets 540 are then
inserted through the holes 550, 560 and 570, with ends of the
rivets 540 extending above and below the gate 280. The rivets are
then melted, either ultrasonically, thermally, or by some other
conventional means, thus heat-staking the assembly together.
With the present embodiment, the heat-staking is especially useful
because of the localization of the contact pressure for the
electrode contacts in the overlap areas 480 and 490 as shown in
FIG. 21. Thus, good individual contacts are insured, and individual
connections do not have to be separately adjusted, such as by means
of screws and bolts. Because of this, the reliability of the
bimorph gate array is greatly increased, while the labor involved
in constructing it is greatly decreased. In addition, there is a
considerable cost saving in avoiding the use of the nuts and
bolts.
The printed circuit board 470 includes one connection for each
bimorph 200 for energizing the overlap area 265 (i.e., the
high-voltage electrode) via the conductive Z-STRIP 440. It will be
appreciated that the construction of the bimorph is considerably
simplified by the increased thickness of the bimorphs 200, which
greatly decreases the likelihood of bubbles or wrinkles forming in
the bimorphs when they are constructed. This also makes the
bimorphs considerably stronger, with less likelihood of damage
occurring during construction of the bimorphs and of the gates.
Another reason for making the bimorphs 200 thicker is that for
larger optical fibers, greater deflection of the shutter 260 is
desirable, and with thinner bimorphs, the stiffness of the bimorphs
would not be great enough due to the increased length thereof.
Thus, in order to achieve greater deflection while preventing the
bimorphs from collapsing under their own weight, the thickness is
increased. This leads to another advantage of the thicker bimorph,
which is that it needs attachment only at one point (namely at the
glue layer 250), and does not require the use of a separate
fulcrum. Since the bimorph itself is stronger, the mounting is not
so delicate, and the weight of the bimorph at its tip is sufficient
to ensure adequate alignment with the fiber tip, without the need
for a fulcrum.
Shown in FIG. 32 is a block diagram of a system utilizing the
present invention. Once the bimorph gates have been assembled into
an array, they may be utilized in the entire optical system 580,
which may be a video display, a communication array or a point in a
communications network, a printer, or other system or device where
video or graphics information may be utilized or wherein a
plurality of individual optical elements is needed. Thus, the exit
optics shown in FIG. 32 may be a video display terminal for
viewing, a portion of a communications network, a printer, or other
device.
Typically, an array of optical systems or shelves 580 will be
utilized together, such as in a 32-shelf array 590 as shown in FIG.
33. It is preferred that each shelf 580 include 32 bimorphs. In one
embodiment, 16 of the fibers connected to the bimorph gates are
connected into a first fiber bundle, and the other 16 are collected
into a second bimorph bundle. This is shown conceptually in FIG.
34, where bundles 600 and 610 are shown. The optical fibers from
bundles 600 and 610 are connected to the gates 280 (which are not
shown in FIG. 34 to preserve clarity) in an alternating fashion.
Thus, a fiber from bundle 600 is connected to the left-most gate, a
fiber from bundle 610 is connected to the second gate, a fiber from
bundle 600 is connected to the third gate, and so on. In this
manner, each pair of gates on each shelf 580 includes one fiber
from bundle 600 and one fiber from bundle 610. As will be explained
below, these pairs of gates comprise half-pixels 620, designated by
the circles in the lower portion of FIG. 34.
Two adjacent shelves 580 in the array 590--one on top of the
other--form a matrix of pixels which is one pixel high and sixteen
pixels wide. This is because each half-pixel of the upper shelf 580
in the pair of shelves includes two fibers from two different
bundles, and the half-pixel of the lower shelf directly below it
includes one fiber each from two other fiber bundles. Thus, in FIG.
35, an upper shelf 580U includes fibers 630 and 640, and a lower
shelf, 580L includes fibers 650 and 660, with fibers 630, 640, 650
and 660 in the aggregate forming a pixel 670.
Inputs to the optical fibers of the shelves 580 are connected
source optics 680, represented in FIG. 32 and shown in FIGS. 26 and
29. Referring to FIG. 26, a lamp 690 is provided, preferably
providing white light. A mirror 700 (referred to as a "cold
mirror") is interposed in the light 710 from lamp 690, and is
designed to transmit infrared radiation 720, while reflecting the
visible portions 730 of the light 710. A fan 740 creates a moving
body of air 750 to cool the mirror 700 and the other portions of
the source optics 680.
In an alternative embodiment, as shown in FIG. 29, a different
mirror 760 is utilized, which reflects infrared radiation 720, but
transmits the visible portion 730 of the white light 710.
A filter tray 770 is mounted so as to intersect the visible portion
730 of the light, and includes several (preferably four) filter
holders 780, 790, 800 and 810, as shown in FIG. 27. In one
embodiment, the colors of these filters are, respectively, red,
green, yellow, and blue, as designated by the letters R, G, Y and B
in FIG. 27. Alternatively, the filter in filter holder 800 may be
green, which would be typical for video display uses, wherein the
green light source is often doubled up, because it contains most of
the luminance, and this increases the effective resolution of the
display. Many other filter combinations, utilizing other colors,
are possible.
Connected to the filter holders 780, 790, 800 and 810 are fiber
bundles which are coupled at their other ends to the gates
contained on the shelves 580. Thus, fiber bundles 600 and 610 are
connected, respectively, to filter holders 780 and 790, and
additional fiber bundles 820 and 830 are coupled to the filter
holders 800 and 810, respectively. As described above with respect
to fiber bundles 600 and 610 relative to shelf 580 shown in FIG.
34, similarly fiber bundles 820 and 830 are connected in an
alternating fashion to an array of bimorph gates on another shelf
580, forming an array of half-pixels. For instance, fiber 630 shown
in FIG. 35 may be part of fiber bundle 600, fiber 640 being part of
fiber bundle 610, and fibers 650 and 660 comprising part of fiber
bundles 820 and 830, respectively. In this case, fiber 630 would
carry red light, fiber 640 would carry green light, fiber 650 would
carry yellow light, and fiber 660 would carry blue light, if the
filters shown in FIG. 27 are utilized.
It will be appreciated that, if each shelf 580 includes 32 bimorph
gates, and the array 590 shown in FIG. 33 includes 32 shelves 580,
there are a total of 1,024 optical fibers utilized by the array
590. Since each pixel 670 shown in FIG. 35 comprises four optical
fibers, there are 256 optical fibers for each filter color shown in
FIG. 27 (or, alternatively, FIG. 28), and thus each optical fiber
bundle 600, 610, 820 and 830 includes 256 optical fibers. The top
shelf 580 in the array 590 shown in FIG. 33 will have 16 red-light
optical fibers connected to it, and 16 green-light optical fibers.
The second shelf 580 in the array 590 will have 16 yellow-light
optical fibers connected to it, and 16 blue-light optical fibers.
This alternating pattern continues to the bottom of the array
590.
Referring to FIG. 32, when the lamp 690 is energized, each of the
optical fibers connected to the array 590 has light of the
appropriate color provided to it, and thus each of the 1,024
bimorph gates has light provided to it. The pattern of opening and
closing the gates by means of the printed circuit board 470 (shown
in FIG. 18) determines the display appearing at the exit optics,
such as at front face 840 of the array 590. The control hardware
shown in FIG. 32 provides the necessary information for opening and
closing the bimorph gates, and is operatively connected to the
printed circuit board 470. Such hardware may include a
microprocessor, memories, and other conventional hardware for
driving information systems.
An alternative to the filter tray 770 is shown as filter wheel or
filter tray 850 in FIG. 30. The filter tray 850 may include several
differently colored filters, such as red, green, blue, yellow, cyan
and magenta, as represented therein by the initial letters of these
colors.
In this embodiment, at least four different lamps would be
utilized, with one fiber optic bundle connected to each lamp. Thus,
four lamps 860, 870, 880 and 890 are utilized, as shown in FIG. 31.
The filters contained within the filter trays 850 may be rotated so
that a single filter is utilized, and the other filters are
excluded. Thus, the filter trays 850 shown in FIG. 31 are "dialed"
to red, green, yellow and blue, respectively, from left to
right.
Represented in FIG. 31 are four modules 900, 910, 920 and 930. Each
of these modules comprises two shelves 580, and as represented
schematically in FIG. 31, each module is served by all four lamps
860, 870, 880 and 890. The red-light fibers (represented by the
lines from the left-most filter tray 850 in FIG. 31) are connected
to all four modules 900-930, as are the green-light, yellow-light
and blue-light fibers. Thus, each module of two shelves is provided
with light from different lamps, with a ratio of four lamps per
four modules. In an array of 32 shelves, this would include 16
modules, and a total of 16 lamps in the embodiment. Other ratios
are possible, such as one lamp for each color to supply all 16
modules, for a total of four lamps for 16 modules.
Other embodiments of lamps, filters and modules are possible. For
instance, each of the modules 900-930 may alternatively be a single
shelf. There may be a configuration wherein the four lamps 860-890
have the same filtration or no filtration (resulting in a
monochrome display), or where the lamps 860 and 870 have one
filtration, while lamps 880 and 890 have another filtration
(resulting in a two-tone display).
FIG. 36 shows an alternative embodiment of the invention, wherein a
"super pixel" is utilized. Rather than using four optical fibers
per pixel, as in FIG. 35, an array of the first-order pixels 670
may be controlled by the control hardware to operate as a single
super pixel 940, which in FIG. 36 comprises four individual
first-order pixels, i.e. 16 optical fibers. It will be appreciated
that in the embodiment of FIG. 35, each optical fiber may be "on"
or "off" depending on whether its associated bimorph gate is open
or closed. Thus, there is no provision for different intensities of
the pixels, for a given pixel color combination. However, with the
embodiment of FIG. 36, there will be four red-light fibers, and
four fibers each for the colors blue, green and yellow. Thus, the
intensity of the red light may be varied in five steps, including
no red light, and from one to four red-light fibers exposed. The
same is true for each of the other colors, so considerable
variation in intensity may be achieved.
The super pixel line 40 of FIG. 36 is thus a 2.times.2 array of
first-order pixels. Other arrays are possible; for instance, in a
6.times.6 superpixel, there would be 36 fibers for each color, and
37 variations in brightness for each color (including all of the
pixels being off, and 1 to 36 pixels being energized). This will
accommodate a large variety of desired video displays.
The alternative embodiments utilizing superpixels are highly
advantageous for the following reasons. In order to generate a
variety of intensities using a pulse-width modulation system, the
reaction or "rise" time for an individual bimorph must be very
quick. For instance, if 256 bimorphs must be driven at a rate of no
less than 60 Hz (for video displays) each bimorph must react within
a time of 1/256.times.1/60=65 microseconds, or 0.065 milliseconds.
That is, at 1/60 of a second per frame, there must be 256
sub-periods for the entire scan. Given gate response time of, for
example, about 8 milliseconds, the fastest the bimorph can respond
to a refresh signal is approximately 125 Hz. Thus, intensity
variations utilizing the bimorphs with such a response rate would
be impossible at normal video frequencies. The superpixel
construction, however, allows full video capability even with the
slow rise times for the bimorphs, since the intensity variations
which must be accommodated are no longer time-dependent, but rather
are dependent only upon the number of fibers within a super pixel
which are energized. Thus, signals with both color and brightness
information may be provided in parallel to the bimorphs, with no
loss of video display speed and no dependence upon bimorph rise
time (so long as the rise time is at least as fast as 60 Hz).
Furthermore, the intensity variations possible are dependent only
upon the number of pixels used in a super pixel, and thus are
limited only by the available sizes of optical fibers and the size
requirements for the display or other exit optics.
An alternative embodiment of the invention is shown in FIGS. 37-41.
In this embodiment, a bimorph gate assembly 1000 is shown in a
sectional elevation. A substrate 1010 carries an optical fiber 1020
in a groove thereof. Raised portions serving as heat stakes 1020
and 1030 are provided on the substrate 1010 and may be unitary
therewith.
A lower printed circuit board 1040 is mounted on the substrate 1010
and conductive rubber strips 1050, 1060, 1070, 1080 and 1090 are
mounted atop the circuit board 1040, as shown in FIGS. 37, 39 and
41, and described in detail below.
Mounting inserts 1100 and 1110 are positioned on either side of
heat stake 1030, as shown in FIG. 37. A bimorph 1120 of the same
design as bimorph 200 described above is positioned atop the strip
1050, and bimorphs 1130 and 1140 are similarly positioned atop the
conductive strip 1070 and 1090, respectively, as shown in FIGS. 37,
39, and 41. The bimorph 1120 is preferably in contact with the
mounting inserts 1100 and 1110, and is glued to a top surface of
the insert 1110 to provide a pivot point.
Positioned across the tops of the bimorphs 1050, 1090 are zebra
strips 1150 and 1160, which are conductive along the lengths of
conductive traces on a bottom surface of an upper printed circuit
board 1170, as shown in FIGS. 37-40. The zebra strips 1150 and 1160
are conductive in the vertical direction shown by the double arrow
in FIG. 40 and are also conductive in the vertical direction from
the point of view of FIG. 37, but are not conductive along their
lengths, i.e., to the left and right from the point of view of FIG.
40. That is, the zebra strips are conductive along their widths and
heights, but not along their lengths.
High voltage traces 1180, 1190 and 1200 are provided on the bottom
surface 1175 of the upper printed circuit board 1170, as shown in
FIG. 40, and a multiple-contact ground electrode 1210 is also
provided on the bottom surface 1175. Connected to the ground
electrode 1210 is a common trace 1220. Referring to FIG. 42, it
will be seen that in the preferred embodiment 32 high voltage
copper trace electrodes are utilized on the upper printed circuit
board 1170. FIGS. 40 and 42 represent "X-ray" views of the circuit
board 1170, i.e., looking down through the top of the printed
circuit board with the copper traces appearing as though the
circuit board were transparent. The ground electrode 1210 is shown
in FIG. 42 to have two common traces 1230 and 1240, which are in
different locations from the trace 1220 shown in FIG. 40. There may
be one or many such common traces, at a variety of positions on the
circuit board 1170, with FIGS. 40 and 42 showing two possible
embodiments.
As shown in FIGS. 37 and 38, zebra strip 1150 contacts the high
voltage electrode portion 1250 of the bimorph 1120, which
corresponds to the overlap portion 265 of the bimorph 200 shown in
FIG. 16. Zebra strip 1150 also contacts the high voltage electrode
portions 1260 and 1270 of the bimorphs 1130 and 1140, respectively,
which are shown in FIG. 41, and similarly contacts the high voltage
electrode portions of the other 29 bimorphs which are utilized in
connection with the high voltage copper traces of the circuit board
1170 shown in FIG. 42.
Zebra strip 1160 contacts the ground electrode 1210 at numerous
ground traces 1280, 1290, 1300, 1310 and 1320, and additional
ground traces as shown in FIGS. 40 and 42, with one ground trace
corresponding to each bimorph 1120, 1130 and 1140, etc., and with
one such ground trace corresponding to each high voltage electrode
1180, 1190, 1200, etc., such that each bimorph is electrically
coupled both to a ground trace and to a high voltage trace of the
upper printed circuit board 1170.
It will be understood that one or many ground traces such as ground
traces 1280, 1320 may be utilized. If zebra strip 1160 is replaced
by a homogeneous conductive strip, it is possible to utilized a
single ground trace, such as ground trace 1280, and the conductive
strip will electrically couple all of the bimorphs to ground. One
conductive rubber strip or pad--such as strips 1050, 1070 and
1090--is also provided beneath of each of the bimorphs in the array
of bimorphs (preferably numbering thirty-two) beneath the printed
circuit board 1170. A continuous copper layer 1330 or other
conductive material is provided on a top surface of the lower
circuit board 1040, as shown in FIG. 39, such that the conductive
rubber strips or pads 1050, 1070, 1090, etc. couple the lower sides
of the bimorphs to a common ground. It will be appreciated that
conductive strips 1060 and 1080 are redundant, in that they contact
the zebra strips 1150 and 1160, further coupling them to ground
with the common trace 1220, but do not directly contact any
bimorphs. The copper layer 1330 may be connected to ground
independently, or may be connected to ground through the conductive
rubber pads or strips 1060 and 1080, etc. by coupling through the
zebra strips 1150 and 1160 to the common trace 1220. One such
conductive rubber strip will suffice; however, many such strips may
be provided, allowing for redundancy and reliability of the ground
connections. Similarly, ground traces 1290 and 1310 are redundant
ground traces, and these may be omitted if the copper layer 1330 is
independently grounded, or one to many such traces may be
included.
A top or lid 1340 is attached to the bimorph gate assembly 1000 as
shown in FIG. 37, and is "heat-staked"; that is, stakes or rivets
1020 or 1030 are ultrasonically, thermally, or otherwise heated to
rivet the assembly 1000 together in a fixed fashion, while pressure
is maintained on the top 1340 and on the substrate 1010 to ensure
reliable electrical contacts which seal off gas, liquids and
corrosive materials. The stakes 1020 or 1030 (and it will be
appreciated that a large number of such stakes may be provided)
protrude through holes 1350, 1360, and other such holes as shown in
FIGS. 37, 40 and 42. Each hole such as 1350 and 1360 includes a
first area of a smaller diameter for receiving the heat stakes, and
a second area of larger diameter, as shown in FIG. 37, such that
when the heat stakes are heated, they melt slightly into the areas
of larger diameter to form a permanent assembly 1000.
When the assembly 1000 is completed, the shutters of the bimorphs,
such as shutter 1370 of bimorph 1120 shown in FIG. 37, are
positioned just in front of the forward edge 1380 of the substrate
1010, and just beneath the top stop of the lid 1340. A lid stop and
mounting guide 1390 is preferably provided, and is preferably
integral with the substrate 1010.
The structure shown in FIGS. 37-42 has the advantage that the
contact points of the rubber strips, zebra strips, printed circuit
boards and bimorphs are concentrated in very small areas, thus
providing high reliability of these contacts and good sealing
against corrosive materials. The conductive rubber strips such as
strips 1050, 1070, 1090, etc. are preferably somewhat narrower than
the bimorphs 1120, 1130, 1140, etc., in order to avoid accidental
shorting between the edges of the bimorphs and the conductive
rubber.
FIGS. 43 and 44 show another alternative embodiment of the
invention, utilizing bimorphs 1400 and 1410 of the same design as
bimorph 200 shown in FIG. 16. In this embodiment, the zebra strips
and conductive rubber strips are replaced by conductive buttons,
such as buttons 1420-1480. These conductive buttons are mounted on
the lower printed circuit board 1490, which is of the same design
as the lower printed circuit board 1040. Similarly, the upper
printed circuit board 1500 is of essentially the same design as the
upper printed circuit board 1170 shown in FIG. 40, except that the
conductive traces may be of a different configuration to
accommodate the conductive rubber buttons instead of zebra strips
and homogeneous rubber strips. Overall, the embodiment of FIGS.
43-44 is essentially the same as the embodiment of FIG. 37, but for
the substitution of the conductive buttons for the conductive
strips of the latter.
As shown in FIG. 43, a single conductive rubber button is mounted
on the bottom of each high voltage electrode such as electrodes
1510 and 1520, and contacts the high voltage electrode (of the
exposed center layer) of each bimorph, such as electrodes 1530 and
1540 of the bimorphs 1400 and 1410, respectively.
Similarly, conductive rubber buttons 1440, 1460 and others are
mounted on the bottom surface of the upper printed circuit board
1500 so as to contact both the top ground electrodes 1550, 1560,
etc. of the bimorphs 1400, 1410, etc., respectively, and to contact
the top of the lower circuit board 1490 (such as by means of the
conductive rubber button 1450). Finally, lower common connector
buttons 1470 and 1480 are mounted on top of the lower circuit board
1490 so as to contact the lower ground electrodes of the bimorphs,
such as lower ground electrode 1570 of bimorph 1400, as shown in
FIG. 44.
The embodiment of FIGS. 43 and 44 further confines the force which
is applied to the bimorph assembly (such as bimorph assembly 1000)
upon construction to a yet smaller surface area, thus increasing
the pressure applied at each of the connections. This makes for a
more reliable electrical connection at each conductive rubber
button, and ensures good sealing characteristics. It will be
appreciated that only a single common conductive button 1450 is
necessary for contact between the ground electrode common trace
1505 of the upper printed circuit board 1500 and the top conductive
surface of the lower printed circuit board 1490; however, many such
buttons may be used for redundancy and reliability.
It will be noted that the connections with the bimorphs in the
embodiments shown in FIGS. 15-42 have surface areas which are
substantially equal to or (in the case of the button connections)
less than the surface areas of the electrodes of the bimorphs.
Thus, where conductive rubber pads or zebra strips are utilized,
the pads or strips are laid transversely to the longitudinal
directions of the bimorphs and to the electrodes on the printed
circuit boards, which results, as discussed above, in confining the
force of contact to small areas, thus ensuring reliable and
fluid-tight contacts. Where the conductive buttons are utilized, it
is likewise preferable that they have diameters which are equal to
or less than the diameters of the bimorphs and the printed circuit
board electrodes, and have areas which are substantially less than
the areas of the bimorph electrodes and the printed circuit board
electrodes.
The embodiment of FIG. 43 and 44 has the additional advantages that
only a small amount of conductive material (such the conductive
rubber buttons) is required, and costs are thus reduced while
reliability is increased and assembly is greatly simplified.
In a preferred embodiment, an alternative configuration of filters,
light sources and bimorph gate arrays may be utilized, as shown in
FIGS. 45-48. Referring to FIG. 45, an optical source 1580
preferably provides white light to each of a plurality of bimorph
arrays or modules 1590, 1600 and 1610. Of course, many more such
modules may be used, and they are preferably arranged as described
above relative to FIG. 33. A color filter array 1620 is positioned
at the output end of the modules 1590-1610, and exit optics 1630
are provided which may be any of the devices mentioned above
relative to optical system 580.
In this embodiment, all of the filtration is accomplished by the
filter array 1620 at the output ends of the bimorphs, instead of at
the input ends. The filter array 1620 includes a matrix of various
colors, such as the matrix of red, green, blue and yellow filter
windows 1680 (designated R, G, B and Y, respectively) shown in FIG.
47. Thus, the filter array 1620 is a filtration mask providing
filtration in any pattern and using any number of colors
desired.
The array 1620 may be photographically formed, in the following
manner. A sheet of photographic film 1690 (for instance, a standard
16 cm..times.16 cm. positive transparency film) is exposed to the
chosen colors by using masks 1640, 1650, 1660 and 1670 represented
in FIG. 46. Mask 1640 includes exposed portions 1642, which in this
embodiment are red in color, and opaque portions 1644. Likewise,
mask 1650 includes green exposed portions 1652 and opaque portions
1654; mask 1660 includes blue exposed portions 1662 and opaque
portions 1664; and mask 1670 includes yellow exposed portions 1672
and opaque portions 1674. It will be understood that, if the film
1690 is a negative film instead of a positive film, the colors of
the exposed portions 1642, 1652, 1662 and 1672 are chosen
appropriately (namely, the complementary colors are chosen) to
produce the correct colors in the array 1620 upon development of
the film 1690.
Each mask 1640-1670 is placed over the film 1690, one at a time,
before the film 1690 is developed, and is exposed for a length of
time chosen to produce the desired intensity of the filter windows
1680 upon development. The opaque areas of each mask prevent the
areas of the film 1690 which underly them from being exposed. Thus,
the film 1690 is exposed four times in this embodiment, once for
each of the masks 1640-1670, such that after the fourth exposure,
substantially the entire sheet of film 1690 has been exposed, with
no two colors overlapping due to the patterns of the masks. The
filter array 1620 is formed upon development of the exposed
film.
The photographic masks 1640-1690 may take on any of a variety of
colors and configurations, including configurations wherein the
colors are designed to overlap. Such masks are easily generated by
standard computer-controlled apparatus.
The embodiment of FIGS. 45-48 has the advantage that all of the
bimorph shelves or modules 1590, 1600, 1610, etc. may be identical,
such as the module 1590 shown in FIG. 48. Since the filtration is
provided only at the exit optics of the modules, there is no need
to differentiate either among lamps for the optical source 1580
(which need provide only white light) or among the modules
themselves, which may have 32 fibers placed in the grooves of the
shelves, all for receiving and transmitting the white light from
the source 1580. The intensity of the light transmitted from each
bimorph array is controlled in the manner described above.
Therefore, in this embodiment there is no need to utilize separate
fiber bundles such as bundles 600, 610, 820 and 830 shown in FIGS.
26 and 29. A shelf array such as array 590 may then be constructed
with the fibers all being interchangeable and undifferentiated.
This results in a much simpler and less expensive manufacturing
process. In addition, since all of the fibers may be bundled
together, and a single light source may be used, a simpler, more
uniform and more efficient optical coupling to the fibers
results.
Although the invention has been described in terms of the preferred
and alternative embodiments disclosed herein, those skilled in the
art will appreciate many changes which could be made to these
structures and methods without departing from the scope of the
invention.
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